Where is the nearest doctor on a Sunday

I've been in bad pain on and off for 3 days(today being the 3rd) I am wondering where I should go to see a doctor on the island or mainland,I would go to the hospital but you can't get a bus back if you arnt seen by 5pm and when I burp I can taste blood,I think I may hae an ulcer that is bleeding,I had an appointment with my doctor last week who told me I was anemic and that my white blood cells where down,so I'm really worried and I'm in agony,anyone have any suggestions as to where I should go???