"Weak erections" are not caused by masturbation. It doesn't work that way. If someone told you that it does, they were lying to try to keep you from being sexual. Your penis is made so that you can release and get an erection. That's why it's there and why you have it. It won't break if you make it do the task at hand.
If your erections get weaker all of a sudden, you must be having some other health problem. It could be linked to your hormones, nerves, blood flow, or even stress. You are avoiding the real cause of the problem when you say it is masturbation alone, and it will get worse.
In any case, I think you should see a doctor, explain what's happening, answer their questions, and do any tests they suggest. They are going to figure out what's wrong with your body and use all the power of modern medicine to help you.
