Having more kids?

My hubby & I have been together for 13 years. We have a son (7) daughter (3). My hubby really wants another baby. I do not. My reasons are (1) finances (2) we both work really demanding jobs (3) we don't have a lot of family support (4) I am currently furthering my education. We have discussed this several times. I know that he will always long for another child. Whereas I am completely satisfied with the 2 we have after suffering a miscarriage. & 2 threaten miscarriage while carrying our dd. Am I being selfish?