My Gf And I Had Sex About 2 Weeks Ago

My gf and I had sex about 2 weeks ago before her period. She felt a bit nauseous sometimes and is a little tired too. She got her period 4 days late but it came and ran it's course. Now that she's been off for 2 days we had sex again and she was a bit tighter than usual an got sore quick plus she says that she hurts more than usual. Might I add shes been taking birth control for almost 4 months now. Is this just the pill? Or is she pregnant?