My boyfriend and I have been having unprotected sex 3 to 4 times a day at least for the last five days and about four days after sex I have started to feel a little nauseous and my lower stomach just below my belly button has been feeling a little achy and I have been having some mild cramps and lower back pain as well is there a possibility I could be pregnant?

Too soon to know... you have to be at least two weeks late for your period before you can take a test... and it will be even longer before you might get moning sickness...

So it might be something you ate at this point making you feel that way.