Hm. Well, chest pain should always be checked out. At your age, a heart issue is not terribly likely. But you need to make sure. Your heart beating faster when aroused is probably happening. Angina is another name for chest pain and during or after sexual activity is a time some people have it. Here's an article to read but notice the ages in the article. Much older than you. https://www.health.harvard.edu/heart-health/matters-of-the-heart-sex-and-cardiovascular-disease However, I'd get checked out. Make a doctors appointment and tell them what is going on. And get the green light to start light exercise. That will benefit you overall. Your heart is a muscle that needs exercise to be healthy. And being overweight is hard. It can be overwhelming to think of losing weight but if you take it slow and just work at it a little each day, you an achieve that goal of losing some pounds. Even losing 10 pounds improves heart health. So, can you see your doctor?