I got pg the month after we lost C. We weren't trying exactly but we weren't being careful either - iyswim. I was quite surprised that I got pg so quickly as I'm quite a believer in mind, body and spirit. However another bereaved mummy told me that her Doc told her that bereaved mothers often fall pg very quickly after they lose a child. Maybe it's the body's way of trying to heal the mind and heart?
The pg brought with it a whole host of feelings that were hard to deal with at the time (eg was I trying to replace C? If I could swap this baby and have C back I would), but I had a wonderful mw who listened to me ramble and cry and helped me make sense of what I was feeling. As the pg progressed the rational side of my brain took over from the emotional side and I realised that I would never be able to replace C. He was irreplacable.
What I/we yearned for was of course to have C back, but what we really needed was to be a family again (C was our firstborn). M gave us back that again.
C is C, and M is M. My whole body still yearns for C, but M has not filled the gap C left, he never will. And for me, that is a good thing.
But as Shabs said, M gave us fresh hope and a renewed purpose. I do not regret for one heartbeat having him so quickly after losing C. But, everyone is different and you have to decide what is best for you. Sod what everyone else thinks, it is your decision.
I hope this gives you some food for thought, and please feel free to ask any question you want. If you can't ask it here I don't know where else you could