Hey OP
I have a baby who is 16 weeks and following slimming world before pregnancy too, what I've been doing is batch cooking on a weekend so her dad can look after her for an hour at a time and then I'll batch cook two different meals one day and two on the other.
Or I cook when she is asleep (although she can be a bit of a cat napper tbh), I'll start by just chopping up all the vegetables and getting all the ingredients out of the cupboard that I need, so if she wakes I can stop easily. The actual cooking itself doesn't take that long, it's more the chopping.
I batchcooked loads the last weeks of my pregnancy (I was actually 12 days late so if helped me keep my sanity) and I couldn't believe how wonderful and helpful it was to have those meals there once we had the baby.
Are you breastfeeding OP? Because there have been points for me where it's been impossible to cook on a weekday because my baby was feeding so frequently, but for me it's slowed down a little now
Another thing I've been doing is wearing a Moby sling and putting her in that when she's due to go to sleep, bouncing around a bit and then if she falls asleep I get on with cooking. Obviously you do need to be particularly careful with this suggestion but it's a good way to get on hands free. I got my sling off eBay before baby was born second hand for £20
I have been losing weight very slowly and it actually has stalled a few times probably because It was Easter and then mine and my partners birthdays, so I was eating too much chocolate. But I put on three stone three pounds by the end of my pregnancy and I now have one stone exactly to lose to get back to my pre-pregnancy weight
I've not been following slimming world though, I've been having cereal with chopped banana in for breakfast, then at lunch I'll have a tin of soup or eggs, some crisps, fruit, cereal bar and dinner either one of the meals I've batch cooked (jambalaya, chilli con carne, bolognese, chicken & vegetable pasta etc) or more recently I'll make something super easy. I'll put a bake potato on before my partner gets home and get the topping ready, usually beans or tuna and grate some cheese and put it all to one side so if I need to feed baby my partner can take over.
Another one I've been making is pasta bake, I have been using the jars though but it's very convenient for getting some more veg in, i chop everything, weigh out pasta when I get a chance in the day then throw it all together around five to stick on the oven.
I would just say try not to eat/buy high fat snacks and try not to eat too much bread and you should see things going in the right direction eventually
Oh i also got an ergobqby carrier and try to go out once a day and walk the dog, even if it's only a half hour walk it's something. I haven't been doing everyday though, not like before she was born.. I think it just takes time for you to get back to what you were doing before. Your life has been turned upside down and you need a whole new routine and everything. Just been kind to yourself don't expect to be perfect all the time, just make small changes