My husband is taking pain meds for a work injury, and we can't seem to conceive. Is it due to the medication?

Could be. Medications can interfere with erection and ejaculation, sperm count and motility, and fertilization. There are, however, many other causes of infertility that should be investigated. Best to review all medications with your fertility specialist.
Unlikely. I very much doubt it, but what's the injury and what is the medicine?