There are a variety of reasons that sex can be painful after birth. It may be pelvic floor muscles that are still too taut, injured, or spasmed. There may be some nerve damage that is still healing. In those cases, allow time for recovery--and do be in touch with your health care provider if you have questions or don’t think you’re progressing.
If the mother is breastfeeding, there’s can be a reduction in estrogen that contributes to vaginal dryness. In those cases, a silicone lubricant (Pink Silicone is our most popular in this category) can be very helpful.
In any case, I encourage new mothers to be forthcoming in their follow-up medical visits: Returning to a comfortable sex life is, ideally, a part of the new family “normal”! Whether or not your health care provider asks about your sexual health, please bring up your questions or concerns.