I think you are saying that you have recently been having sex for 4 days in a row while you were also taking some type of drug. And now you are having a problem with maintaining an erection. Normally, a 20 year old should have no problem getting an erection. But a couple of things can give you problems. If you have had a lot of sex for those 4 days, your body just may need to rest a while - like 3-5 days. Then you should be better. Also, many drugs can have a side effect that will cause sex problems. Both recreational drugs (pot, heroin, etc) as well as prescription drugs. If the drugs are from a doctor, talk to him about using a different drug. If the drug is just for fun, maybe stop using it. Good Luck!!