Unplanned and uncertain

This is my first pregnancy and it was completely unplanned for us. My fiancée has been amazing and is just absolutely ecstatic about having a baby, whereas I feel like I'm still adjusting and not as thrilled or excited. I feel like an awful person for this sometimes. We have talked about having kids before, but I just don't feel ready. I was suppose to have another 2 years before we started trying, if that's what we decided we even wanted, and I think I'm struggling with the fact that that choice has been completely taken away from me. The potential of things that were to be in these next two years is gone, my life plan upheaved and turned on its head and I'm still just reeling from understanding that reality. Anybody else having an unplanned pregnancy and have feelings like this? I feel like such a monster some days for being upset or unhappy. I try talking to my fiancée but he just doesn't get it. These hormones aren't helping either.