Help fistular and constipated for 14 days !!?

Im a 22 year old girl who got a ingrown hair and this caused a small abcess the abcess then made a fistular which I had surgery to lay open i now have a massive wound all the way to where you go to the loo! I left hospital with instructions to eat lots of fruit and veg and wholegrain drink lots etc to produce a healthy bowel movement.. within 3 day i was desperate to go but wen I tried i realised that through pain there is no way i can go to the loo i ended up passing out and being sick just from trying!! .. we are now 14 day on and all my doctor will offer me is senna but as i explained its not that i cant go cos I can its i litrally have to clench to stop myself as im scared of the pain !! stuck what to do !! :-( so uncomfortable !!