You are pumping at too high a level or for too long if you are getting fluid build up.
Ideally you should not be seeing that except as a sign that you are overdoing it.
You can certainly take erection enhancing drugs, provided of course that you are healthy enough to take them in the first place.
The pharmaceuticals you mention carry the danger of a severe drop in blood pressure if you take too much, so be careful. If you take a single dose of one or the other it may make it a bit easier for you to get hard and to regain an erection after you’ve cum. And some folks do report harder erections, particularly with Viagra, but if you have pumped yourself silly, to the point of a spongey dick with fluid build up, no amount of Viagra will make that go away until the lymph system carries it away. An erection (however it is achieved) will serve hasten that process, though. And you should be able to get hard enough to have sex in any event.
The headaches come from congestion, most likely. It’s good to drink a lot of water when using these drugs. I also take a Mucinex, I’ve found that helps too.
Before: I'd like to show you something I'm very proud of, but you'll have to move real close.
After: I\'d like to show you something I\'m very proud of, but you guys in the front row will have to stand back.
God gave men both a penis and a brain, but unfortunately not enough blood supply to run both at the same time. - Robin Williams (: