Play it safe and make an appointment with the pediatrician!
I second that, always better to be play it safe. Just be sure to warn the clinic ahead of time that he has/ had the chicken pox recently and may still be contagious. You don't want to sit in a waiting room infecting everyone. Chicken pox can be dangerous for some and you never know how immunocompromised some people are in those rooms.
Thanks for your replies. I took him to the doctors as i found another lump on the back of his neck. She said he has swollen lymph nodes caused by the infection but the one on his rib is in a funny place but there is nothing to worry about?!
Swollen lymph nodes usually go down on their own once the infection clear. I'd just watch it as the pox leave, make sure they're leaving too.