Trust me, once you're in the middle of the worst of the withdrawals, you won't care about having to take prescriptions. It's worth it to take something prescribed for opiate withdrawals, I'm talking about for three days tops. You WON'T be able to sleep at all and your blood pressure will be through the roof. Clonidine isn't habit forming, but it does lower your blood pressure and helped me with withdrawals. I also took Tranxene prescribed by my doctor for a very short period of time. Potentially habit forming, but weak as far as benzos are concerned, and she only gave me enough to take during the absolute worst of the withdrawals.
If you're determined to only do OTC, tylenol PM or something may help for some people but was futile for me. Hot baths help, as cliche as that sounRAB. Some people say that benadryl helps them get a little bit of sleep, but then other people say that it just makes them tired but not able to sleep, which can be even more annoying. I really think it's worth getting a couple day's worth of Clonidine or Seroquel even to help with sleep if at all possible. You won't get addicted to these drugs and they will make you feel a little less like crawling out of your skin, that awful, jumpy feeling that accompanies O. withdrawals.