I know there are a bunch of these, but I don't want to worry myself over something that could be nothing. 

I am currently 21 years old, and going through school (lots of stress). 

I have had sex back in the middle of December, without a condom, but my boyfriend told me that he had stopped (like stopping a stream of urine). So I was really irritated that he didn't use a condom and had finished inside me. I had immediately gotten up to the bathroom and had gotten whatever I could out before going back to bed. Earlier in the day, I had a pain in my side from what I had thought was an egg releasing (I get those sharp pains about every month that I end up having a period.) my period was expected in two weeks, but did not come (I am very irregular, but had a normal cycle sept, oct, and nov.) I had taken a HPT in january and another early february. Both came back negative. Later in feb, I had what I had thought was my period (right on schedule as it would have been, and same flow and about the same length) but decided to take another HPT in march and another first week in april . Again, both negative  To let my mind be at piece, I had visited a private clinic for another pregnancy test and and intravaginal ultrasound. The tech said that she saw what could be some clotting, but if the test came back negative she was confident that I was not pregnant. And it did come back negative. She also felt my uterus for any abnormalities, and said that everything was fine there.

Somehow I am still not at ease because I don't want to be the person who doesn't show, or the tests come back negative when in fact I am pregnant. I have been feeling bloated when I eat even the lightest meal. My breasts did feel sore late december/january, but has since passed. I do not feel sick in the morning, or I focus too much on it that I think I feel even the slightest bit sick, and start to worry. My back hurts every once and a while, but I don't know if its due to doing schoolwork , or when I am at my job (backroom at target, so I'm moving around alot.)

Any input would be great, as I am just looking for any advice that I can get :(

Thank you so much!