Can Surgery,morphine And Unprotected Sex Cause Delayed Period?

i'm a 17 year old girl and i have very regular periods, most times it even comes early, but lately 4 weeks ago on the 27th of april, (just at the ending of my last period) i was in hospital just about to go into surgery, and after my surgery i was taking morphine tablets for a few weeks after to kill the pain of surgery. also i'm very athletic and since surgery i've been sitting at home heaps, i've done a bit of research and these causes can delay or skip periods, but i also had unprotected sex one week befor my period, the guy pulled out though. i was just wondering if it's more likely i'm pregnant or my cycle is just messing up because of the drugs and physical changes since surgery. (it's been exactly 4 weeks since my last period)