I have been on synthroid of 50 mcg for 4 months and now 75 mcg fo...

I have been on synthroid of 50 mcg for 4 months and now 75 mcg for about 3 months. I do forget to take it now and than, but otherwise been pretty good about it. I am 30 yrs old, and also take vicodin and flexorill for my back. Can someone tell me if the synthroid is causing the extreme tiredness and fatigue i am feeling. Note - I dont take vicodin or flexoril until about 11 pm at nite. Only on synthroid during the day. It is so extreme that I almost went to the hospital. Thought I was going to faint.