I am extremely confused and thinking okay if I am not pregnant something is clearly wrong with me

Okay, this is going to be long so I apologize in advance.  

This all started back in February, so about 2 months ago.  On February 15 I noticed some blood after I went to the bathroom and assumed it was my period, though I was immediatly concerned because my period was not due for another week and a half.  This was about one week after I had ovulated and I did have sex on that day.  My periods are normally 5 days, heavy on the first few and then gradually lighter.  This time it was only extremely light and lasted for 11 days!  They have always been consistent and never more than 5 or 6 days.  On the 11th day it just abruptly stopped (usually it tapers off).  I dismissed it and thought maybe it was just a weird period due to stress, as I have been more stressed out than usual.  However, I soon began feeling very nauseus and it was hard for me to get food down but then I started to get really hungry and then bloated, especially after eating.  After doing some research on implantation bleeding with pregnancy, I began to worry that maybe it wasn't a period after all and it was actually implantation bleeding.  So off I went to the store to purchase some pregnancy tests.  I bought First Response Early Response and took one the next morning (followed all directions, using first morning urine) and it was negative.  Now at this point and from my calculations (yes I know that you calculate from the first day of your last period)  I would have been 6 weeks which means plenty of time had passed in order for a pregnancy to show up on a home pregnancy test, let alone and early detection one.  I took a second one the next morning to be sure and it was also negative.  So now here I am extremely confused and thinking okay if I am not pregnant something is clearly wrong with me.  The following month in March I did get what seemed to be my period again but it was also irregular.  This time, though it was heavier like a normal flow, it seemed to only last 3 days.  

I have been to a number of doctors and not one of them can tell me what is going on with me.  They all tell me I am fine and dismiss me as just being overly anxious, then they proceed to prescribe me anti-depressants.  They did blood work and everything was normal and withing range with the exception of a slightly elevated bilirubin level for my liver.  I was told that this is normal for me considering the bloodwork I had done back in December (because I was having and increase in migraines) was the exact same level.   I was also tested for Lupus because my Grandmother died of it but it came back negative.  I also went to Urgent Care because I became concerned that maybe I was having a relapse of Mononucleosis that I was diagnosed with back in 2009.  My results were normal.

New sypmtoms seem to pop up every day.  I am extremely itchy in various parts of my body, mainly my neck and shoulders/upper back, stomach, and arms.  There was no rash at first but now I am noticing tiny little bumps.  It is not all over my body just in certain spots.  It comes and goes.  I'm having difficulty sleeping.  I wake up in the middle of the night feeling like I can't breathe (I was told this is nocturnal panic attacks), my overall anxiety is through the roof, I can't focus on anything, I am getting EXTREMELY lightheaded and my vision gets blurry and unfocused and feel like I will pass out and when this happens I get really shaky and my sinuses get blocked up and I get really agitated and don't want any interaction whatsoever the slightest touch irritates me.  The bloating comes and goes.  I would be almost 12 weeks pregnant now if that is what is going on.  I haven't tested again since I did at 6 weeks weeks but I have read that home pregnancy tests just don't work with some women for whatever reasons and that they have monthly bleeding throughout most, if not all of their preganancies. 

I feel like I am losing my mind.  Were the tests false negatives?  Has this ever happened to any of you or do you know of anybody this has happened to and if not, what do you think could be causing all of these symptoms?  I just feel really off and like I am living in a fog.  Is this all stemming from the mono that I had 5 years ago?  Could it just be anxiety?  I don't want to sound wacko but should I request to be tested for parasites?  I just want some answers because I can't take this anymore.  I'm scared that I am dying!! :(   It is really scary when you know that something is wrong with you're not getting anywhere with doctors. Any thoughts and advice are much appreciated, thank you!