Welcome to HCM,
Your weight depends on your height,but 313 pound it is really good that you want to lose as your weight is more you need lot more calories and you may be also restricting your diet .
Before you start any workout you must get a medical check up to see blood pressure and other metabolic disease if there is any in your case.
If every thing is fine even genetics may be responsible and you can even consider a surgical option called bariatric surgery
Please continue to take care of your diet and regular work out as it is key to long term success.
Take professional help of dietitian to get good nutrition.
Best of Luck