I have the same problem with walnuts. It kinda feels like an itchy-burning sensation, similar to when you eat too much pineapple. It goes away after about 10-15 minutes.
I grew up thinking that everyone got this feeling when eating walnuts, it wasn't until college that i mentioned it and someone told me that it wasn't normal, and that I had a mild allergy.
Two things to note is that food allergies can be mild like that, and that they can develop over time. Just because you weren't once allergic to something, it doesn't mean that you can't develop an allergy.