Do u think im being selfish?

hi, my head is really messed up at the mo and need some advice from an outsider. me and my partner have been together 4 3 yrs now and we have a 23 month old together, im 24 and hes 20 but were both very mature and grown up 4 our ages!, i have 2 other children from a previous partner which causes no problems at all, we are a perfect little family only i cant get out of my head the fact that i want another baby!!! i've always said i'd like 4 only where the 3 are so close togther i wanted to plan it so theres no more then 3 yrs between the last 2, but my partner says he's not ready which i can sort of understand cause of age, but i've only 2 mnth left 2 achieve it...he says yes in a few yrs maybe but 2 me its 2 late, the youngest is already spoilt by his family and i worry what effect it will have on the other 2 growing up as their fathers not interested.
also i would love to become a midwife 1 day so i dnt want to start then fall pregnant, i'd love 2 get baby 4 out the way 1st then all grow up close and happy togehter. he keeps messing with my mind as well tho, i've been askin for over a yr now, 1 min he says yes then no, 4 months ago he said we could try in 2 months but then said no. its really got to me emotionally. i love him so much but i fear i'll loose him if i push him but i cnt help it, its what i want! the only reason he can give me is that he doesnt want 2 be a 20 yr old with 4 kids...what do i do, if it was to split us up, id loose out anyway as i only want him 2 be the father but staying is making me feel anger for him for not doing this for me! sorry for waffling...lol. please help!!!!!!!!!!

Give him time

I can see where he is comeing from having four children 2 care for and provide for at 20 is a big ask(when alot of 20yr olds are down the pub!)I think that you should sit back give yourself a break from havin kids and re think babys another year or 2 down the line because if you do it may turn out that your on your own with 4 kids be happy with the family unit that you have,why dont you look into the training to be a midwife now that would give you a project to get stuck into