Written by Emily Nagoski, Ph.D.
Lower desire, more pain and mental noise about body image stuff is endemic among post-partum women; it's all normal, but that doesn't always make it easier for either person in the relationship. So what can you do? Figured I might as well let ya'll know what I told folks:
Ian Kerner wrote a book called Love in the Time of Colic (best title ever), which may have some answers. There's also the fantastic book From Ouch! To Ahhh...The New Mom's Guide To Sex After Baby by Sarah Swofford, a sexuality educator with an MPH degree. And I've actually found that the best advice for helping women cope with giant traumatic changes to their bodies is the original G Spot book by Alice Ladas. She's a body worker who wrote as clearly as anyone ever has about the ways that life events impinge on sexual functioning. It wont seem immediately relevant, but it is. Start with those books and see if they help.
My own advice is STOP HAVING SEX. Make it a rule. A game. You can cuddle and caress and fondle and kiss but no genital contact and definitely no orgasms in front of each other. You can make up any variation on these rules that work for both of you, but they must take away all anticipation of/dread of sex.
Bear I'm mind there's a lot of conflicting stuff happening in her body and mind. Pregnancy, birth and breastfeeding completely overhaul a woman's body. It's like taking a field of grass and turning it into a vegetable garden. You can't just lay there anytime you want; there's maintenance to do! She lives in a brand new body and has to learn how to be sexual in it, at a time when she's massively sleep deprived, stressed, and distracted by (let's face it) higher priorities. Sex is like planting petunias in that vegetable garden. It would be nice, sure, but WE ARE GODDAMN BUSY WITH OTHER THINGS AND CAN I TAKE A NAP NOW?
You don't need sex toys and or lube right now. Remember SIS and SES? Lube and vibrators stimulate SES (gas), when what you really need is to remove all stimulus to SIS (brakes). That's stress and worry of all kinds, including worry about physical pain and about your feelings and desires.
To conclude: replace sex (temporarily but entirely) with affection. Read those books. See a doc if the pain doesn't get better. And forget about making things More Sexy and work on making them totally joyful and relaxed.