What Are The Side Effects Of Norlevo Pills?

I took Norlevo on the 18th of April. I had heavy blood loss for 5 days after. Ever since then I feel constantly severely dizzy and faintly. I also have headache and heavy headed feeling. Is it serious? What should I do? Thank you.
I'm 40yr old, medium height, light weight (45kg) female. I'm in fairly good health condition otherwise, just slightly underactive thyroid which is treated with Thyroxine and under control.