My husband wont have sex with me

I do not know if it's a valid problem but I do think it is... Just a little back story-- my LIP and I have 1 7-month old baby and we have a 15-year age gap. I am younger. It's a little frustrating na my 40yo husband wont have that much sex with me. We only intercourse once a week and then almost close to a quickie. When he comes, even if Im not yet done (and Im not done ALL the time)-- we're done. And then 1 round lang. It gets frustrating. How do i tell him.