The only way of raising your metabolism is to raise your T3. Has it ever been tested? If not, it might be a good investment to have a private test - FT4 and FT3 together to see if you're converting OK.
If the FT4 was that high, and you're still not losing weight, the odds are that you aren't converting that T4 to T3 - the active hormone. And, by the way, you're only over-medicated if your FT3 is over-range, but doctors are too uneducated to know that.
In fact, doctors are so ignorant about thyroid that a lot of us end up medicating ourselfves. If you can't convert T4 to T3, the only thing you can do is buy your own T3 and take that.
You cannot kick-start your metabolism by eating smaller portions more often if your T3 is too low. It just doesn't work that way. The odds are that your extra weight isn't even fat, so dieting won't have any effect on it. However, it could make things worse...