What Causes Severe Dizziness?

Hi. I m having some symptoms of concern. The Nain one being I am feeling cronicly light headed. It s about half the day, comes and goes pretty constantly but the stench of the feeling increases and decreases to bearly noticable. It s made worse if I move my head suddenly like to look up, or simply roll my self over in bed. When I kissed my boyfriend I felt it increase a lot more as my heart speed up a little. I stopped taking my synthroid medicine about a year ago exactly. I was homeless and couldn t get it together to see a doctor and renew it. I thought maybe there related but this is all of a sudden since about 2 weeks ago. It s gotten slightly worse over the last 2 weeks. I could be pregnant but it would only be maybe 2.5 since conception if that s true. I m on the pill.