I had this problem too, just sort of circling around the ring then standing and trading with them which suited them perfectly. Instead i just forced myself to box them, constantly moving in and out moving on my feet all the time trying to make new angles. Throwing a combination then getting out quickly, then launching another combination. Generally they will want slower paced trading as then their reach advantage comes in full effect. You have to start using your speed, make them off balanced by being unpredictable. Practise your footwork so you can turn your opponant and gain the middle. This is what my coach told me to do and it worked wonders for me against people heavier and lighter i was able to out box them and helped me personalise my style which suits me now. Fight your fight not theirs and you will regain your skill again.