Should i try to get pregnant again?

OK here is the scoop, I am encroaching on my 40th bday and I am dealing with a" fertility crisis". My husband is 50. I have a 7yr old healthy but hyper boy and a 9 month old boy who may have a developmental delay. The reason for the gap is allot of looses 2 with a possible genetic issue (geneticist unable to determine @ this time). Yes I am tired emotionally and physically (being an advocate for my little one and getting his needed services). However I always wanted 3 kids and I feel incomplete. My husband is done as far as he in concerned. However, I don't think that would be an issue if I wanted to pursue a pregnancy. We cannot afford to adopt. Should I stop being selfish and direct my time,energy and money to the 2 I have already. Or should I try to complete myself and possibly endure more heartache of a loss or another special need child? Leaving it to the info train. Thanks