Further Test??

My son (aged 2) has 3 enlarged nodes in his neck, one over 2inch long and pretruding, and one in his groin.  He has seen the pedritician and they have said that 2 in his neck and 1 in his groin are all within the normal limits (although the one is larger than a grape?) the one that is longer than two inches she said was larger than normal but felt ok to her.  They did a blood count (normal) and test for glandular fever and told me to not worry.

This was last week, and I can't stop worrying - especially when I am sure that the large 1 is still growing and I know that the blood test can't rule out lymphoma.  I pray that I am worrying for nothing but until they're gone I won't be able to stop.

Do you think I should ask for further test or just accept the doctors opinion and do my best to forget about it?