Brief Answer:
Small Penile fracture?
Detailed Answer:
Hi,
Almost certainly you have what we term 'penile fracture'.
Most likely your erect penis was thrust forcibly against your partner when you were manipulating for a more convenient position. Sometimes, the fracture is a massive one where all the congealed blood which is present at the time of a normal erection in the tubular engorged structures called corporae cavernosae leaks out through an opening in the lining of the corpoare and causes immediate loss of erection and pain with patients and partners describing a 'popping' sound.
You must have had a much smaller defect in the lining of the corporare due to which you were able to complete your act at that time, but there must have been persistent slow ooze and that has caused your present level of discomfort and even the induration in your
phallus.
You certainly need to see a
urologist who specializes in these matters, and get some basic investigations done. These could include an
ultrasound examination of your penis in both flaccid and erect states, and if required also 'cavernosogram' and retrograde urethrogram, following which we will be in a better position to advise you. For the moment, I would suggest that you do not attempt intercourse till things have become clearer.
I do understand that you might not want treatment for this problem and see if things get better on their own, but we cannot be sure that will happen, and secondly, even a natural healing could cause some sequelae like a curvature of penis or persistent
pain during intercourse which I am sure you will not find acceptable especially since you are still fairly young.
Hope I have been of help.