What Is The Painful Bump On The Side Of Head?

My 16 year old daughter noticed a painful bump on the lower left hand side of her head. I ve kept a close eye on it and haven t noticed any abnormal coloration. It feels to be the size of large pea. There isn t any other symptoms. This is really concerning us. At first we had considered it to be a pimple. Just curious what your input would be. Thanks in advance