Why is it so hard to climax???

I’ve only ever finished twice with two other men. My husband of 3 years I’ve probably finished 4-5 times. When I do finish it’s because I’m on top and having to chase it HARD. Like my core hurts from the way I’m having to crunch to get it. I’ve tried to relax , I’ve tried to put in a ton of effort and at this point I’m just frustrated. We’re basically only doing it for him , I mean it’s enjoyable during the time it takes for him to get there but I just have no energy to do it. Im having some major thyroid issues and I just have no desire. When I do get my hopes up that I could finish I have to try so hard and then it’s not even fun anymore. Is there something I can do?? Anyone with thyroid issues, when it’s removed does that help??