Weird symptoms the dr.'s can't seem to pinpoint what it wrong

I've been sick for over three weeks now. It started out with nausea and a little vomitting and then a little congestion and slight cough, but nothing that would make me think that I even had the flu or cold or anything. Dizzy spells and now it's just twitching muscles at times in my abdominal area going towards my back and extreme pressure to lungs when breathing although all tests show normal oxygen level. I've been to the ER and they said everything came back within normal ranges. Feel better when walking around as apposed to sitting or laying down. Laying down much worse. General feeling of malaise and I'm getting so tired of being sick. My thyroid level was a 7 when I was in the ER and they told me to take 1 1/2 pills a day (1.25) and that was two days ago on Monday. I felt much better yesterday and thought that was the answer to my problems, but I've had a bad bad day today and have the muscle twitching now and just ache. Breathing has been way more labored today. Could this be a wicked virus? Would it take a month to get over and if it's my thryoid will it take long to regulate? I just don't know how much I can take. I just feel bad all the time.