Well, there isn't much you can do about getting old. Once I hit my mid-30s, I started noticing things in bed "fell flat" a bit after a healthy drinking bout so I acquired some 20mg sildenafil through one of those phone app services and it works great for me. I don't know what dosage you took but definitely go as low as possible. I'd say 100mg is way too strong to begin with and could be why you're getting headaches. I started off trying one 20mg pill sober and it was pretty effective; 20mg drunk as fuck, however, wasn't as much of a party; and I've found that two 20mg pills about an hour before action and with my last couple of drinks is the key, and no headache at all.
I would also strongly advise against Cialis, as I tried taldalafil a few times and while one dose lasted for two or three days and gave me a raging, 1992-esque half-hour-hard-on if I even looked at my dick, it also gave me an absolutely wicked headache and nasty heartburn for days.
I've been told (by friends, not doctors) that vasodilators, like Viagra, by virtue of how they increase blood-flow, are what give you the headache; therefore, if headaches are an issue for you, try taking a bit of a vasocontrictor, and the easiest one to find is caffeine. Friends of mine tank a Red Bull with their generic Viagra and they claim it helps.
Barring that approach, I suppose you could try a cock ring? I've never bothered since I've got a key fob full of generic pills if I party too hard for my own good and I also think they look quite bizarre. On top of that, those rings are quite thick and cumbersome and I'm ethnically 100% Japanese, which means every centimeter matters and I can't afford to lose the precious real estate.