Yes it is entirely OK to feel that way

unfortunately we go thru bouts of feeling lousy like that and envious of those who are where WE SHOULD BE. You're still grieving the loss of your little one, the emotions involved with that are so irratic and irrational to us as times, boarderline confusing.
I was hesitant to open this post only because lately has been harder again as well, hugely pregnant ladies newborns and pregnancy thrusted into my "bubble" as I'm severely missing my angel. Should be in my 23rd week right now, somehow I think you and I are probably within days of each other... sept 23rd here