What can I do for the pain after a pulpectomy?

Call your dentist. Did you have root canal treatment started and did they specifically call it a pulpectomy? A pulpectomy is something that is done when there isn't enough time to do root canal or endodontic therapy. It will often reduce pain until you can return for more complete treatment, but there may be pain too. If you weren't prescribed pain medication, contact the dentist who started your treatment.
Depends. It depends on the pathological status of the pulp before the pulpectomy was performed.If you had an inflamed pulp, take 3 advil (ibuprofen) evert 3-4 hrs as needed for the pain. If you had an infected pupl( necrotic) you may need an antibiotic in addition to pain meds. In a few days the pain will subside, gradually decreasing after the first day.
Pain relief. You can take 3 advil and 2 tylenol (acetaminophen) every 6 hours for the pain, if these are safe for you. You may also need an antibiotic for an infection.
Normal healing. Remember that you've just undergone a surgical procedure. It will take between 2-4 days (normally) to heal from such a procedure. But, when it finally does you should feel a great sense of relief. Often the discomfort associated with surgery is noticeably different than the toothache which necessitated the pulectomy. If not, call your dentist immediately to report your findings.
Call your dentist. Your dentist should be able to prescribe pain meds, if he has not already done so. He also may want to prescribe antibiotics.