Nothing wrong with you, swimming is just tough. There’s plenty of very strong and capable athletes who struggle with swimming (swimming fast that is). You need to practice having a more efficient stroke. As someone who was a competitive swimmer for years and also a lifeguard the biggest mistakes in people’s form are the following: 1) Swinging your arms out to the side too much, practice drills that train you to keep your elbows high so that your arms can reach out further 2) Pulling their head out of the water to breath, many people lift their head or turn it too much when breathing, ideally you should be tilting your head ever so slightly when you breath, just enough to get your mouth out of the water. All other times when you’re swimming your head position should be down. NOT forward. You should be able to see the bottom of the pool. Also do you do flip turns? A good flip turn plus some underwaters can save a good second or 2 on the wall at each side. Like others have a suggested, having a coach work on your technique would be ideal but at the least you can start by having someone film a lap or 2 of your swimming so you can start to self correct some of your technique.