Why can't doctors agree on my diagnosis?

Since I was 17, I have been in some form of therapy and on some type of medication for depression.  I am now 52 and 5 years ago I became so ill I had to stop working as I could not cope with anything.  I was given all sorts of different cocktails by my G.P. who also wud see me once/month for one hour for "therapy".  I decided to go to see a phyciatrist and was given different meds, cognitive therapy but nothing long term.  Then I was told I cud participate in the day hospital and did so for 2 weeks before I received a job offer which I really needed to support my boys.  This job lasted only 8 months.  After only 1 month I was asked if I was on street drugs as my hands were shaking and they said I was a totally different person from the first time I had worked there 6 years earlier.

Again, another job down the drain.  I haven't worked since and 4 years ago I fell and had to have a back operation which was not a success, therefore, pain meds were added.

Several doctors have told me I am bi polar (my father and 4 of his sibling have) and some don't.  So I am given meds that I know are not helping as I am at the lowest point of my life. I suffer from terrible side effects - dry mouth, weight gain, sleepiness and sleeplessness.

I really don't care what the name is but why can't anyone get it right?

Any suggestions pls?