Am I pregnant? When time frame does conceiving take place? Help?

Okay, so my main question requires some attention, my boyfriend and I spent valentines together, very romantic and made love that night... But, I can't remember when I went on my period, It's been a very stressful few weeks so I've been very forgetful! I'm utterly nervous when I'm supposed to go on again. It's been two weeks since and I think i usually go on my period around the end of each month or the first week of the beginning. Although this is usually when I go on my period, my boyfriend said he remembers me going on it around the middle of January. I'm panicking. Birth control is not an option. What is the time span of conceiving? What should I do?