Why Am I Having Severe Abdominal And Back Pain?

I am about three weeks pregnant and after a home test that confirmed it. Monday night I felt very hot and after that I woke up with severe abdominal pain and at times back pain. If I then go to the toilet to pass urine at times especially after the pain there is drops of blood about two or three and at times I spot on the tissue. The abdominal pain and backache becomes less painful if I place a hot water bottle over it and it can disappear for hours or for the whole day. I do not have a fever and I do not feel nauseas and its only Monday night after taking mild painkillers that I bled heavily after urinating. I have since stopped taking the painkillers.