Is it normal to have stomach pain after taking plan b?

Yes, that's normal. As are any hormonal symptoms. You could get things like nausea, tiredness, cramps, leaking/sore breasts, back ache, bloating, spots, mood swings/depression & many other symptoms. Most pass within a week or two. It's a big dose of hormone for your body.
You may have some bleeding, which could be anything from spotting to a full blown heavy bleed for days. Not everyone bleeds though.

A couple of tips, in case you didn't know:

*Hold the teat of the condom closed whilst it's rolled onto his penis. This prevent air getting trapped in it, & causing the condom to burst during intercourse. If there's no air in there, it can't pop.

*Always hold the condom on the base of the penis as he withdraws. This stops it sliding off inside of you.

*Never continue to have intercourse once he's come, with the same condom still on him. As soon as he loses his erection, the condom will stop being tight, & will either slide off inside you, or leak into you.