8 days late, negative test results , some pregnancy symptoms, but weird period ?? please help???

Hi, i know im kind of late on this thing but i really need some advice?? My last regular period was June20th-25th i recently started having sex some time in the middle of june, but i then had unprotected sex with my boyfriend on july 14th where as he pulled out but i kind of felt as if he was a bit late, anyhow he masterbated a bit after he pulled out and then went back inside of me and we continued having sex where he then pulled out again... a couple days later i felt very lightheaded and dizzy but i felt that it was because of the heat because my mom said she felt the same way as if she were going to pass out, one time i actually threw up but i also believed that it was because of the heat. I was expecting my period to come on the 20th of july but when it didnt come i kind of started freaking out like can i be pregnant? I then decided to take a hpt on the 24th of july where it came back negative i drank 2 full bottle of water just to get to pee in the first place. I still had my doubts about it because i read so many stories of women that had negative test results both blood and urine and were still pregnant. On the 26th of july i had a pregnancy blood test done and it to came back negative. I tried to continue on with regular life since both test were negative but i was to afraid to smoke or drink until my period came. My period then came on the 28th of july at about 4am with the cramping and everything but the flow seemed a little different the flow was just a bit off but i considered it as normal i guess but started to lighten up withen the day, i changed my pad with in the next 2hrs and there was about a thumb print of blood, the next day it was the same light blood and it kind of started to look brown afterwards it just stopped i didnt even have to wear a pad anymore. i did notice that there was a little blood when i wiped(pinkish color) but nothing to wear a pad for. On day 4 it was kind of dripping blood in the toilet after i peed so i decided to put a pad back on (sorry for the details) but it still wasnt alot afterwards so i took the pad off hours after because i had noticed it was just spotting then it stopped. On day 5 I had sex and after when he was done he pulled out and there was like this brownish blood on the condom, i cleaned up after that and then started crying because i was scared. I forgot to point out my symptoms, im nauseas everyday around the same time at night i kind of feel like im peeing more then usual and my back is killing me i was actually really bloated especially on the 30th of july but then the bloatedness stopped i still feel nauseas everynight and my back is still paining me i've been crying alot because im worried that if im not pregnant then its something 10x worse i also have been taking these death naps in the middle of the day and going to bed early. Oh yeah i had an ultra sound done on the first of August and her words exactly were "i dont really see anything, i dont see a sac either" some times i feel this little pinching feeling in my right side, and some times i kind of feel this pulling feeling in my stomach i also had this migraine from hell and i have on and off headaches that dont last to long aswell. Im extremely worried, i cry everytime i think about it and i just want to find out whats going on with my body because i know my body and this certainly doesnt feel anywhere close to normal, any advice and or comments will be greatly appreciated. Thank you.