Feeling for my sister

I am 36.. about to be 37. I was pregnant once before and had a miscarriage but i felt the same for my sister that time too. So here is why I feel some type of way.. She is 39 and has been hoping to get pregnant for sometime now. We are very close and I would love to be pregnant simultaneously! I believe in God and His will so I understand that it's not up to us, but I feel bad sometimes when I talk about or get excited about my baby, due 12-25-18. I know she is happy for us and she is not "jealous" of us.. but i can't help but remember the disappointment I felt each time I started my period and I had to wait to try again. I hope she gets pregnant!! Prayers.. God's will is better than ours but I just don't know why I feel badly for her..