small penis is not a problem but the matter is that is your potency normal or not, due you get erected on sexual arousal or not are you able to sustain erection for certain period or not and are you able to ejaculate normally or not.
so first of all you should note that is your penis get erected in the morning just before waking up or not because nocturnal and early morning erection is a common physiological phenomenon and if you lack it then you might have some organic cause for which you really need treatment.
donot get depressed because of short size as this is actually not a problem for proper intercourse, but if you really have impotency then you can get your blood testosterone
, FSH and LH level done and then you can take androgen therapy like testosterone injection 250 mg IM once a week for 3 injection , subsequently lengthening the interval between them.
certain exercise can strengthen your penis and pelvis muscle so for this you can consult a physiotherapist.
you can take some drugs like oral sildenafil
for erection problem just before intercourse but that's to after consulting a clinician as this drug have several contraindication .
I hope your most of the doubt are now clear and donot hesitate in consulting a physician as they are to help you.
bye and thanks.