The reason you can't lose weight is because you are over-exercising and under-eating.
With a TSH of 3.25, your FT3 is going to be low. Exercising uses up T3 and makes the FT3 even lower. And, if you aren't eating enough calories, you aren't going to be able to convert more T4 to T3.
I don't know where you've been researching, but T3 is not a weight-loss drug. True, it needs to be optimal for you to stand a chance of losing weight. But, how can you possibly say that T3 is the answer for you, if you don't even know what your T3 level is? If - and I know this isn't true - but if your FT3 were at the top of the range, and you started taking T3, you would make yourself ill. Plus, it could even make you put on more weight, because you need to be on the right level - not too low and not too high. So, just blindly taking T3 is not a good idea.
Before you even think of T3, get your ducks in a row. Get an increase in T4 and bring your TSH down to below one. Optimise all your nutrients. Then get the Frees tested to see just how well you're converting. If you're converting badly and your FT3 is low, then taking T3 will be a good idea.