Too scared to be happy... is this normal?

Sarah • Married my best friend 11/12/13. We have 4 boys ages 8, 5, 5, and 3 (no they aren`t twins... we are a blended family).
I finally got my BFP after almost a year of TTC. We've had 2 MC (December and May) and 1 chemical in July. I'm 4w2d today and so scared. I want to be happy and excited, but I can't seem to get past the fear of losing this one too. My husband doesn't understand why I'm so scared, he says I shouldn't be. I'm hoping and praying that this will be our Rainbow Baby. I have to go Monday and Wednesday for blood work to test my HCG levels, and I'm not sure I can handle the results if they aren't getting larger... and now they are putting me as "high risk". Is it normal to feel like this or am I overreacting?