Gastri pump failure

I'm male, 81 years old, TURP followed by 40 radiation treatments for early prostate cancer 25 years ago.   Procedures successful in eradicating cancer cells but a lot of attendant, peripheral damage to bowel and urinary systems.   I've managed quite well in spite of periodic bouts of diarrhea and severe constipation.   Twice within the last dozen years or so my stomach "shut-down."   I had to have my stomach pumped.  (NOT a PLEASANT experience.)   A vague  answer from my family doctor:   "you took too much anti-diarrhea medicine and as a result NO peristalsis; no emptying of stomach. "  I take 4 Lomotil pills a day;  lately on occasion I have added 3 or 4 Immodium tablets in the evening after multiple bowel movements.   My  gastroenterologist tells me to take 25 mg Doxepin at night (years ago he had prescribed 25 mg in the morning and 50 mg at night; and after the last stomach pumping I stopped taking Doxepin thinking that perhaps it was the main "culprit"  in causing gastric pump failure.)   I have to take laxatives to avoid severe constipation.  Crazy.....no.   Laxatives, but anti-diarrhea medicine, also.  I hope that someone might shed some light on my probolems.  
Geneiebug.