You should definitely see your primary care doctor
or your OB GYN doctor about this issue as soon as you can.
The urine pregnancy tests that you get in the pharmacy are usually quite good and should pick up a pregnancy by this point. They are not very good in the first couple of weeks after becoming pregnant, but since you had sex 5-6 weeks ago, they would almost certainly be positive by now if you were pregnant. Therefore, I think the chance you are pregnant is pretty low.
Therefore, it is important to see your doctor. They may repeat the pregnancy test, but they will also perform a complete examination, including a pelvic examination. One of the conditions that they will be very concerned to rule out is pelvic inflammatory disease, which is a sexually transmitted infection of the reproductive organs. This condition can be treated with antibiotics, but it can cause serious long term problems if not treated, including chronic pain and infertility.
The will also want to consider the possibility of ovarian cysts and endometriosis
, which are other common causes of pelvic pain. Most likely they will order some basic urine and blood tests and they may also want an ultrasound
of the pelvic organs. Again, please see your doctor soon!