Why cant I get things out of my mind?

Not sure where this post will go or what it will cover but I really just need to vent. The last few days havent been good for me depression wise and I have been trying to hold it together for K's sake.
Monday I go get a second opinion at another dentist because the first one I saw was a Quack! At least in my book. The new dental place is much better (K recommended it) but with good service comes a hefty price and I fear among other things that my insurance isnt going to consider their fees "reasonable and customary". The worst part is though, that they did confirm some of what the first dentist said and that I need LOTS of work on my teeth. Among things like pulling 2 wisdom teeth and another tooth. 2 sessions of periodontal cleaning to save my gums and supposedly 2 crowns, though I am going to have to draw the line at this one. Crowns alone would cost me $500 each IF the insurance covers the rest of their cost. It just has me soooooo depressed because my last $2,500 I had saved from my divorce settlement was suppose to last for a long time and hopefully be used towards K and I buying a house someday. Its all the money I have left and may cost me all of it to save my teeth. All the other cash from my divorce got eaten up by my move down here....It just scares me so to be broke for one thing.. One of the reasons I got divorced was my Ex always had us deep in debt and I cant stand to live like that. Before I got married I always had enough money for everything AND a savings. Now I could lose everything. Because on top of this, I could very well get slammed by the IRS next year. I have to pay taxes on my alimony and part of my settlement money (some is tax free but not all) and to top it off, I DONT get to claim my son next year, the EX does. We alternated years. *sigh
Then add to my depression the fact that more then anything I promised to take care of K and make her life easier, not harder. I know her parents will begin to hate me if I cant take care of her and I dont blame them. She deserves happiness after all she has been thru and instead she has to deal with my woes too. I know its hard on her because she is trying so hard to not have the pressure of negatives in her life, since they dont help her keep control of her bi-polar; but its soo hard for me to not worry. Its like asking me to just change my DNA.. but I try soo hard for her because I promised I would (and I will do anything) for her.....but I know I am letting her down and that depresses me Most of all.
Now I am faced with another scary situation in my life and I want so much to block it out, till it happens but I dont know how.
Colon cancer runs in my family and I am at High risk because of that and the fact that I have had pre cancerous polyps removed 3 years ago. Now I need to have a colonoscopy done every 3 years and they called today to say I have one scheduled for Sept 13th. The actual procedure doesnt scare me or bother me at all. What has me sooo anxious is the fact that I found out today what kind of pre procedure prep this doctor uses and Im about to throw up over it. Its nothing like my 2 previous ones and seems soo hard on my body, Im shaking just thinking about it. I dont understand why they would need me to do all these things. In the past I cleaned out just fine with 2 small doses of magnisum citrate. This one calls for 3 laxitives 2 days before, then a Large dose of MC in the afternoon, 32 oz of liquid with glycolax in it in the evening, then Another LARGE dose of MC and then 3 more laxitives the night before.... My frigging insides will come out! I dont think I can do it but I cant not have this done because I dont want to die. I just think I will die before I ever get there if I have to do all this. Im scared shitless of trying to do all that (but maybe then I wont have to do any of it LOL... sorry for the bad humor)
But truly I am sooo scared and depressed. I know K will say dont worry about it and just talk to the doctor next week when I go for the prep visit, but I cant get it out of my mind.. Why cant I get things out of my mind?
The final top off of this is K is going to have to take off work to drive me there and back because they sedate me. I dont want her to get in trouble missing work or wasting a day off on me, but I need her there so bad.. I cant imagine trying to do this without her. Because if they find any polyops again, I may have happen what happened last time. A week after they removed them I started bleeding and ended up in the hospital for 2 days. This whole thing has me more of a wreck then K or anyone realizes and I dont know what to do..How do I get thru all this? Why can't I just let it go like K wants me to? Why does my mind not let go?