Is it possible?

Ok so I'm not sure if I should be worried or not... Is it possible to get pregnant if you have sex the same day your period goes off? For the past 3 months all tho I've been worried that I've been missing my period when I went back and checked the time spanned between each period it's been 25 days. The last day of my period last month (30) my partner and I had sex and the day after (31) on the first of February I got sick all day which was odd. And the 25th day that my period should have come on was the 24th this passed Monday. I've taken a test that was neg but I've also been taking energy and metabolism pills which turns my urine highlight yellow so I'm not sure if it affected the results!