hey guys im relatively new to this forum so here goes!

im an 18 year old 5"6, 66kg, budding (wannabe ) mma fighter, ive been doing thai boxing and kykushin karate for a few years and have my first semi pro fight coming up with the UCC (wish me luck!) and was wondering if you guys had any tips for improving my punching power and strength as i dont put on muscle well, i have a small frame but i can hit surprisingly hard with kicks and knees which ill put down to technique from muay thai, but im looking to improve my boxing game because at 5"6 and 18 most people are alot taller than i am compared to what they were when i was 16 as they were the same height! and i need to be able to put some stopping power into some body shots but dont know where to start as for whatever biological reason it takes me an unusually long time to put on any muscle! im not doing this for posing benefits so i dont need anything that improves how my physique looks im happy with how it is im more interested in something that will tip the stand up game in my favour! (hopefully!) greatly appreciate any feedback or tips no matter how small, cheers! danny