I Keep Getting A Pain Under My Left Rib Area/maybe

I keep getting a pain under my left rib area/maybe left stomach area which is driving me mad...what could this be please?...this has been going on for several months now. I'm also getting weird nerve 'attacks' where my nerves seem to contract in a horrible way, I feel suddenly v weak, unco-ordinated & half 'blacked out' & can struggle to breathe freely...& in the last few days I've been getting sudden aches & pains in my joints, especially left knee, left hip, left lower back. These things may or may not be related. Any idea of cause?