Dear prince, THE WAY U EXPLAINED YOUR PROBLEM APPEARS YOU ARE QUITE APPREHENSIVE WITH THIS LET ME EXPLAIN ONE BY ONE.
is a natural and normal activity, in your age group. it doesn't causes any weakness and and other symptoms like headache gi problems and weakness etc. all problems need different attention as for headache you may be having refractive error
get your eyesight checked by ophthalmologist.
for GI problem you may be having IBS
to certain foods find out by observation what food causes the aggravated GI symptoms
other problem shrinkage of penis due to masturbation again i will say the more you stresses the more your penis will shrink. if you remain relaxed it becomes normal.
mostly a psychiatrist
will be right person to help you. nothing is lost in you till you are alive repair system of your body continue to work. don't get depressed in life any time .