new kitten questions

[gabybe]

thank you for your kind help - does anyone know how much he should weigh at 13 weeks - am (sorry being a pathetic new mummy) worried he is underweight as well as he only weighs 1.1kgs (2.6lbs) i can feel all his little bones even tho he has a good size tummy - he was wormed on the 11th May so i dont think it can be that
He is eating, drinking and using his litter tray so no worries there - and yes i have another cat who hates him at the moment but i am keeping them apart
Thought i had posted a picture of him earlier - how do i load more?
:-)