To baby or not to baby?

Brief history; I'm a married mother of 2 boys ages almost 7 & 15.  They are from previous relationships and my current husband and I have no children and he's never been married before and has no children.  We go back and forth as to whether or not to have a child. I'll be 37 this year and even though everyone says I have time I don't have any desire to be pregnant after 40.  By back to the real dilemma; do I even want to conceive again?  There is an internal struggle going on here that only I am suffering; my husband has never bore children so he couldn't possibly understand.  All I can think about is becoming pregnant, being pregnant or planning pregnancy. It's consuming every thought I have!!!  I constantly have dreams about it and it's not  letting off.  I even have these occasional phantom feelings in the breast of the letdown reflex that can only be subsided by my husband sucking on my tit. Sorry I know, tmi.  I feel like I'm going crazy.  I want a baby so badly I can feel it.  BUT, and this is a big but...kids are expensive, time consuming and I have to admit I'm a bit selfish.  Do I really wanna start over now?  I worry my husband will one day regret not having a child of his own even though he says it's not a big deal.  I don't know what to do or why I'm putting so much pressure on myself and the situation other than the fact that my eggs are slowly beginning to perish.  Does anyone else have this emotional/physical struggle? I feel helpless.