Hi OP! I wouldn't beat yourself up at all. You've recognised there's a potential issue there and you're asking for help. I also think you need to have a chat with your midwife - I bet you'll be surprised at how supportive and non-judgmental they'll be!
I was a bit like you. I ate relatively healthily but I often forgot to eat when I was especially busy and really could survive quite happily on a heavily restricted calorie diet. Though it wasn't healthy, it wasn't disordered eating per se as I didn't have negative feelings toward food or my body or control issues; I was just either too knackered to cook (when it's for one, it's harder to summon the energy), or I really did let it slip out of my head and that was easy because my appetite was virtually non-existent due to all the restriction. A vicious circle. But while not necessarily disordered, it is indicative of a lack of self-care that you're right to address.
I think PPs are spot on that it's a good idea to introduce high calorie/fat healthy-ish snacks, rather than making yourself 3 hefty meals a day. You will have to force it a bit at first, I'm afraid, but it is remarkable how quickly your body will get the message and start signalling hunger.
I also think that you need to try and associate some pleasure with food! It isn't just fuel! It's you caring for yourself and your baby, and you can do it in fun, low-pressure ways. If you have space to host, why not invite friends or family for a low key dinner? Something easy and affordable you can prep ahead of time, like a one-pot meal of chilli or a cottage pie etc. (make sure it's people who'll probably return the invite, lol). Or why not meet people for lunch if you have time during the day? If you can afford it, take yourself to a nice place once a week to read a magazine or book while you have a tasty sandwich. If you can start thinking of mealtimes as nice things to do, it may also encourage you a bit!
I also got a bit more motivated about cooking when I met my partner. Do you have someone else at home to cook for? If you do, you can tell them you're interested in increasing your food intake, ask them what they like etc, and try to make it. Loads of recipes online. Watching food shows on TV can inspire too. Junior Bake Off is currently making me feel very superior with my terrible baking skills, lol!