Why can't I get a full anymore?

I'm a 15-year-old guy, and like many others, masturbate. I used to be able to get a fairly hard . A few days ago, I had finished up, and I tried to do it again soon after. I can rarely ever masturbate twice a day, let alone an hour. I failed, and ever since then, my s have been softer. It is still pretty hard, and I can still masturbate with ejaculation, but my no longer stays up fully (I masturbate lying down), it just droops, or flops to the side. Am I getting ED, or can it be attributed to dehydration, lack of sleep, etc? Please answer. I'm getting kind of worried.