I think you identified the problem yourself - excessive porn viewing. You probably then have a desire to get off very quickly when masturbating, and now have kind of 'trained' yourself to respond that way. Try masturbating without using porn, just focus on the good physical sensations, and when you feel you are close to orgasm/ejaculation, stop & let yourself 'cool down' a bit, then resume. You will find over time that you can learn to hold off from ejaculating too soon. Then apply this same technique during intercourse - you have hopefully learned to assess when you're too close & to stop before that point, relax for a moment, then continue. After some practice, you should be able to keep intercourse going for a satisfactory period before ejaculating. Viagra & similar drugs can help you get ready for a 2nd round sooner than you otherwise would, but I don't think it would be all that helpful in delaying things. Try the technique I mentioned & the main thing is not to get in the habit of finishing quickly during masturbation, which many guys do.
Is there any medicine to increase ejaculation time from 1 to 2 minutes to maybe 30 minutes?