How can I get harder erections at 16 years old? I've noticed my erections are getting weak how can I avoid this because I'm sexually active right now.

Performance anxiety? Easy question, "hard" answer. Your erections are dependent on the amount of blood flowing into the venous sinus' of the penis AND the brain stimuli/desire. If you are exhausted, anxious, worried about how "hard things can be" well, erections will not be "easy". By the way, forget about all the men's magazine pill remedies for this, they simply don't work.