I had this exact problem when I got my diaphragm! Even down to going to the doctor (well, nurse-midwife) to get it out. So some things that have helped me:
1) It is hardest to get it out first thing in the morning. I leave it in a few more hours and then try again. My sister says she has to do this too.
2) For a long time, I had my husband take it out. Weird, I know, but it worked, and when the choices were properly presented to him (i.e., help me or we will go back to condoms), we was happy to comply.
I only had this problem for a limited period. I eventually got the hang of using uterine muscle to get it out, but it took awhile (I still can't take it out first thing in the morning - just doesn't work for me). Anyway, I think you can get past this, if you like using the diaphragm. I kind of think about it like when I learned to use tampons - at first, it seemed really hard, but it got a lot easier. HTH