How would i know if my son (14 months old) is having an allergic reaction to peanut butter?

I gave him a ritz cracker that I thought had cheese on it but realized it was peanut butter when it was already soaking in his mouth, so I thought id just go with it. I gave him a couple more within a 3hr period after the 1st cracker. My son has had some congestion & a runny/stuffy nose the past couple days. He just woke up crying (its 5am) and I had to rock him back to sleep (he never let's me do that anymore) should I be worried or am I. Just being paranoid? How would I know, what are signs in toddlers as young as my son?