Do a parasite cleanse. Avoid certain media, porn and arousing activities. Pray more. Fast
Are you currently taking medication? If so did this problem occur before it? It it started after taking medication, some medications for ocd have a side effect that is rare but not unknown of continuous, sometimes painful erections called "priaprism". If you are taking one of the standard medications for ocd such as the SSRI anti-depressents (Prozac, Paxil, Luvox, Effexor) this could be the problem. Speak to your psychiatrist about and ask if that could be what the cause is.