Period? Pregnancy?

So my boyfriend and I had sex two days in a row on my highest percentages days, 27 and 33%, using just withdrawal about mid last month. I didn't realize the days and didn't think anything of it, had my period as usual about a week and a half later. My period was awful, like debilitating, nauseous, ached everywhere, and was generally just miserable but there was not much bleeding. I get super sick every once and a while from my period but it usually comes with heavy bleeding, I thought it was odd but didn't think to much into it. Now a few days past my period and I've been nauseous, bloated, and suddenly feeling baginal pressure.  My question is, can you conceive and still have your period on time or what is going on.