Pregnancy, or maybe I worked out too much?

My Last period was 12/30/2012. I had sex 1/12/2012 where the condom broke and sperm did enter in. since than i haven't had a period, well a normal one at least. each month since then I have had brown discharge/spotting around the time I was suppose to start my period and also had cramps, but no blood. I have took a thousands HPT All negative So I didn't No what to expect. On 02/10/2012 I had the same sexually accident happen, after more negative test I gave up on believing i was pregnant. So I started to see an Ob/Gyn To see what could be the cause and the only solutions he had was that maybe I worked out too much, or maybe I was under to much stress and or my hormones were changing due to the fact I was going through the first years of menstral cycles, but none of those concerned me, because I don't work out, When I do stress I have two periods in a month I never even missed a period, and I been on my period since I was 11 and I'm now 19. So he couldn't give me a legit answer. About 4 weeks ago I began to feel what they call "Bloated" what girls get while on their period I Guess, This was my first time experiencing it and was pretty weird since I never had a stomach my stomach has always been flat and if I Suck in my stomach you can see my bones. Now it's a swollen look just above my pubic area and the rest of my stomach is just starting to expand. cocoa butter has been my best friend since my stomach has been itching non stop. What also freaked me out was my breast have became so heavy and full and my areolas have grown wide and became dark. Since I am a very thin girl I always had a flat stomach and always showed it off. and recently I noticed a brown line traveling from my pubic area to my belly button. It was never there before and so once I seen that I was convinced it had to be pregnancy, I mean no one else can give explanation for it. So I went to The ER and they basically ignored everything I told them, and gave me an ultrasound only checking my ovaries, which made me nerves since the Tech. said she doesnt't know what she ever see's, she just make sure nothing looks wrong... but she did say she didn't see a baby, so now i'm confused! If I was pregnant I would be either 17 Weeks and 2 days or 13 weeks and 2 days something like that... and I'm pretty sure by now something should show up by now... but there is nothing nor any other explanation on what I could be going through. :/
I have/had everything from:

*Morning sickness
*headaches
*fatigue
*Tiredness
*back pains
*Tender Breast
*Frequent (White creamy discharge/ clear stringy)
*Cravings
*Frequent Urintation

So What Can It Be?
NOTE: I Been tested for all STD's, Infection, No Cyst, etc all Negative!

*Sorry for any bad grammer or misspelling I was in a rush.