What you're experiencing is perfectly normal. Women generally need longer to warm up. You can't rush that and you shouldn't. Enjoy the process. You wrote that you hate your body. Don't we all, as women, feel like that so much of the time! Too much of the time. Have you considered turning this around a little bit? Ask your husband what he likes about your body. Maybe the added weight has enhanced your beautiful curves etc. Start to see your body from your man's point of view. Our beauty really shouldn't be marked by the size of clothing we wear. Remember how strong you are, yet soft here and there etc. Think about the good things in your personality. Maybe you're a spontaneous person, or someone who is fun-loving etc.
You wrote that it takes forever to warm up. It's probably because you're really tired from all you do each day while also taking care of a toddler. Sometimes we have all of our touching needs met up when we're holding, touching, nursing, etc a baby/toddler. Your husband making dinner or washing the dishes after (or giving the little one his bath and putting him to bed etc) can be a real turn-on. It gives you a little downtime. The rewards for him (and you) can be huge. Picking a time of the day when your energy is higher, and maybe the little one is napping or otherwise occupied might really help. Middle of the night (if your child sleeps through the night) can be exciting.
You haven't mentioned how you're feeling to your husband because you don't want him to think he has a problem, but in a sense he does. It's not that he's doing anything wrong, but his wife is experiencing something, and that means so is he. I'd recommend talking about it. Not at the moment it's happening, but at a different time of day. Maybe just say something like, 'it takes me so long to get where I need to be in my head to enjoy the moment that I'm concerned you ....' -fill in the blank.
My last thought is maybe you might want to try having your intimate time somewhere else. Make an adventure out of it. If you're a stay at home mom, and really even if you're not, when the moment comes you might glance and notice all the toys on the floor, the dishes that need to be done, and then your mind wanders to the grocery list like you mentioned. If you were to have sex at a place of business that you worked at, during the moment your mind would drift toward work too. It's the same thing for a woman in her home. I think that's one reason to turn off the lights and light a few candles. You won't see the mess so easily.
Just give it time. Relax, you'll get back to where you were. S.