You were 5 days late on your period now your period is 3 days long and heavy but you had sex the day before you started and now you feel like you want to throw up?
Being 5 days late can be from a lot of things. If you are young, and do not want to be pregnant, the stress from thinking you're pregnant can delay your period. Also if you are taking birth control, that can also alter your period. However having a period means that you are not pregnant. On the rare occasion a women will have her normal period during pregnancy, but chances of that happening are unlikely. If you noticed any kind of clots or tissue during this 3 day time frame that you were bleeding then you might have miscarried. Also feeling a lot of pain, almost like you are in labor is another sign of having a miscarriage. As far as the wanting to throw up part, maybe you ate something that didn't agree with you.