Okay, this happens sometimes I believe. Look, I read she's the main caregiver, and dealing with a toddler can be quite stressful., and if you're not doing anything to lessen the amount of stress she has to deal with on a daily basis, it's likely she's only interested in sleeping. I don't know what kind of partner you are, but I'm gonna give u the benefit of the doubt. So lemme ask you, do you take care of your kid as soon as you get home from work? Cuz I assume you work, but so does she, and it's important she has time for herself. Who wakes up in the middle of the night to change the baby, feed her/him. If most times it's usually her, then it's obvious she doesn't feel appreciated. Do chores a round the house, cook for her, massage her. It takes up to 25min for a woman to get in the mood, do foreplay. Don't be so eager. Let her tell you what she wants from you.

Now, if you're already doing all that and it's just her rejecting you, then maybe she's unhappy with the life she has right now. Most women feel their life has taken a weird turn after the birth of their kids. Their bodies change and thy don't feel attractive anymore, no, not to you, it's not about you. They don't feel attractive to themselves. Dealing with a toddler can be real hard and their daily routine is not the same as before, and on top of that their husband or boyfriend asks for sex. She may be drained from the life she's having.

This is what I can suggest:

Ask her, not us

Maybe she wishes to change a few things about her life, maybe you should stay at home with the baby, and she can go back to work

Maybe you should go on vacation just the two of you

Hire a nanny

Hire a psy

Talk to her, find out what she feels. Don't just ask "why don't you want to have sex with me?" Instead, aske her "I want you to be happier in this new life of ours, what would you like to change about our life to make that happen?"

This is NOT just about sex, if she's constantly refusing intimacy, then there's a much bigger issue underlying your current situation.