Doesn't find me attractive anymore

Since the birth of our third child my partner has basically avoided me, he's slept on the sofa for weeks using various excuses. Today I asked him straight what's going on an he said he's not attracted to me since I had the baby. I've gained weight, have loads of strechmarks and I'm the one doing night feeds so I'm looking tired too. I bounced back quickly from babies one and two but not this one, baby boy is five months. I think I might have actually put weight on since having my son ... What am I supposed to do? Lose weight and see if he's attracted to me then 😒 is this just a way of saying he doesn't want to be with me anymore?