weak erection problems? Can self pleasuring cause that?

That's difficult to say definitively. In most cases, no: usually weak erection is related to other issues. In some cases, however, it could be that the penis has become de-sensitized due to rough handling during masturbation, which may make it a little more difficult to obtain an erection. Whatever the case, guys need to keep their tools in good health.  Regular use of a first rate penis health crème (health professionals recommend Man1 Man Oil) helps address issues like soreness, dry/flaky skin, odor, loss of sensation, etc.