Should I Take Femulen Contraceptive Pill Having Missed Period?

Hi I have been on femulen contractive pill for around 8 months now. I have missed three periods. I have done numerous pregnancy tests and they have come back negative. I have been exercising for 2 hours every night to try and lose weight but i am suffering from server swelling in my stomach. my weight can fluctuate by almost half a stone from day to day. is this anything to worry about?