I want a fourth child but my husband doesnt.

How can I get over my husband not wanting another child? yes, we have 3 healthy babies and I'm very grateful for that, but as our " last" is 8 months old and reaching his milestones I feel sad and not fully ready to be done. I'm not one of those to trick my husband into one more or anything, so no worries there. is anyone else feeling this way or have any advice ? * please no rude remarks, really looking for honest advice or similar feelings*