Period 10 days late, all tests negative, severe contraction like cramps, mild dark brown discharge...could i be pregnant with the negative tests?

Unlikely: With modern tests that are very accurate, pregnancy is unlikely. Seek other reasons and perhaps it would be a good idea to see an FP or GYN doctor. They will be able to examine you and determine if you need treatment. Certainly a birth control method would be helpful if you do not want to be pregnant right now. These methods really help control bleeding and cramping too.

AUB?: Could be abnormal uterine bleeding? Have you had unprotected sex in the last month making pregnancy even a possibility? If so, it's a slight possibility you could be pregnant and having either ectopic symptoms or miscarriage symptoms. You should probably also have a gyn exam to determine the source of the old blood (brown discharge) and pain, and while there could have HCG blood test too.