ugh i hate being nauseous....

I been not feeling it all day...my head hurts.. i feel like not eating just nausea..... My period ended 2days ago but i had sex with my boyfriend and i started to bleed again...but dark brown... but now it stopped... i dont know if it has to do with it but also my stomache is cramping.. like my left side... .. 😔should i be worried .. please help i need you guys opinions