Had period for three days but think I am pregnant

Three weeks ago(one of the last days of my ovulation) my Boyfriend and I were messing around and he play his penis with my Vagina but didn't go in. Then he fingered me. There might have been precum on the hand that he fingered me. I read up a lot and I know precum can lead to pregnancy. I really got freaked out. I am still fifteen. I can't have a baby. And I know what I did is wrong. I do not know if it is because of stress or pregnancy, I had been feeling nauseous after that day and my breasts seem to be bigger a bit. I do not know if it is just me or really pregnancy. I felt that there were a lot of gas in me like I burp alot and Fart. But I was just waiting for my period to come.

I had my period but it was three days late. Before my period Come, I had cramps more than usual and notice very very little brown spotting the night before my period come. But my period only lasted for three days. The first day of my period I had very terrible cramps and it was horrible. But I know my period was not implantation bleeding because it is a heavy flow and it is really dark red Colour and have a bit of blood clots in it. During my period my Nauseous become worse.

After my period there was brown discharge and spotting for like three days. And now after my period, I have strange feelings in my Stomach. I have growling sounds and I feel pulses in my stomach and sometimes there is sharp pains here and there. I still have a few cramps but not painful. How ever my nauseous had been reducing. I am having constipation a very bad one. I do not have any other symptoms example those. My breasts are back to normal I think. Is it possible that I am pregnant or am I just worrying too much. Please help.