I was severely asthmatic as a child, (from about 6-8weeks! due to bronchial infection of some kind) I also had a quite bad heart murmur, all that combined had me at the hospital every month for the first 5 years of my life, (seeing a paediatric cardiologist ) I know mum rushed me to hospital a few times as I was blue, wheezing etc.. but it was only ever when I got sick, and when I got sick I got VERY sick.
After I turned 5, the heart specialist gave me the all clear (no surgery) and I seemed to have out grown the asthma too.

I did have a reoccurance of it in my teens, but only because of my stupid decision to start smoking

One of my brothers also had quite sever asthma, he would be on a nebuliser almost every night, but he outgrew it too.

Big huggles Harms, I know it's scary, but you are a super mum and B will be fine do you have an asthma management plan worked out with your paed/gp? ask them any and all questions/fears /worries you have, thats what they are there for!