maternal instinct or just worry?

How do you differentiate between your maternal instinct and just normal worry? I'm 15 weeks pregnant with baby #3, after miscarrying back in October. As soon as I got pregnant this time around I was obviously worried after suffering the miscarriage, but I also kinda felt detached from this pregnancy, almost afraid to buy things or imagine what like would be like when we bring this baby home, and I'm not sure if it's just because I'm afraid to get too attached for fear something will happen and it's unwarranted, or if I truly know deep down that something is going to go wrong. 
So far, I've already had a cerclage placed due to incompetent cervix, so that eased my mind, but on Friday we found out we may have an issue with the umbilical cord attaching properly to the placenta. It's too soon to know if there will be problems but I feel like maybe my fears are coming true. With both of my full term healthy pregnancies before this I don't remember ever feeling this way. 
Does anyone else struggle with this? I'm starting to get really down about this pregnancy, and I'm finding it hard to plan for the future because I'm afraid we will start to prepare and then something terrible will happen. I feel like at 15 weeks I should feel secure that this pregnancy is meant to be and I just don't.