2 day period

The past 2 months I have had a light- medium period that lasted 5-6 days with hardly any cramps. Normally I have heavy periods with bad cramps. My last period was March 9th-13th. I was supposed to get my period around April 4th. Well it was a day late then I started spotting. I had horrible pain on my left side with light bleeding and it only lasted about 2 days and then 2 days of brown spotting. I took about 4 tests and all were negative. I had a few symptoms since ovulation. Cramps, severe moods, heartburn, nausea, headaches and dizziness. I ended up going to the ER because the nausea and dizziness were getting worse. They said I was dehydrated. They did an ultrasound and said everything was fine and said if I was pregnant it wouldn't show up since I would be about 4 weeks. They only did a urine test and was negative. They refused to do a blood test. They sent me home. Had to go back out and get 2 bags of fluids since I couldn't keep enough fluid in me. I feel pregnant but all tests are negative. I had a miscarriage around this time last year and have a 14yr old. I'm only 32. Is it possible to be pregnant and just not have enough to show up? I'm so confused. Never had a period like this. Is it because I was dehydrated or something else?