5.15 TSH level, and your doctor thinks you're fine?! I was practically dead when my TSH test was at 5.0. Does your doctor check your free T4, free T3, reverse T3, thyroid antibodies, AND your TSH, or just your TSH? If all your doctor checks is your TSH, immediately go find a new doctor. The TSH test doesn't even directly measure your thyroid function; it only checks how much thyroid hormone your pituitary gland thinks you need. Ugh.
So what I'd do is go find a D.O. (which is a medical doctor, but with additional training in treating the whole person, not just individual symptoms), or an endocrinologist, and ask for the whole battery of thyroid tests, as I mentioned above. It sounds like your medication needs to be adjusted pronto.
Don't hesitate to switch doctors, though. If your doctor is only looking at a TSH test, and is not treating you by your symptoms first, she is not the right doctor for this issue.
If you aren't already, follow Hypothyroid Mom on Facebook. She posts a lot of great information on this subject.