Had sex on period about 4wks ago. take birth control but he cummed in me twice had cramps and sickness since.can i be pregnant?

Unlikely: Several factors, lack of ovulation being the primary one, make such a scenario unlikely to result in conception. Of course, birth control is only as reliable as the regimen. If you're taking it regularly (e.g. Every day, same time every day, etc..), it's pretty effective. The natural effluent of the menses make it harder for the sperm to achieve its goal.