Pregnant ?!

I'm a week late for my period (which is rare) and a 98% chance im pregnant with my second child as we was trying, I wanted it so bad but now the realation of it becoming realty is making me so nervous/ scared rather than excited? Is this normal?? I'm worried my son who's nearly 2 will play up, not get enough attention , hate the sibling, what if the second child wasn't healthy, all these feelings of doubt,  have I done the right thing?