Is this unreasonable?

So basically my son is 10 weeks born 16/03/19 and I’ve taken a year off work, still with pay but it’s goes down to statuary maternity pay which is just rubbish.

So when I was pregnant me and my partner spoke about money, rent bills everything else and whilst I was still making the same amount of money I’d pay half the rent, I’d buy all the food everything the baby needed and everything for the house. Whilst he payed the other half of the rent and the bills.

We also spoke about him paying more of the rent once my pay went down so I could still afford everything for the baby, and food and stuff for us to have.

So my pats gone down a lot and I’m still paying half the rent which takes a big chunk of money and I’m left really really budgeting my money for the rest of the month.

My partner made a lot more money than me even when I was workin full time. I just don’t know if it’s unreasonable for me to ask him to start paying more of the rent which is what we agreed on?