Jealous feelings over my 9 month old son. am i being silly

ok so i have a little boy of 9 mos and i do consider myself to be a good mum, hes well dressed and has home - made healthy food cooked plenty of love and attention and i stimulate him lots with play and do lots of activities together but the thing is he doesnt seem to like me very much, sure he smiles when he sees me but thats about it! its a very different story with his paternal grandmother when he sees her which is 2 x a week when she lovingly babysits him (which i am very grateful for) his whole face lights up and he cant wait for her to pick him up and when she does he smother her with kissess and loves being with her, when i pick him up he doesnt even smile when he sees me and when we take him home he plays up all night for us which is strange as he has a brilliant routine , its as though he missess her and is annoyed with me for picking him up, i love my son more then anything but i get very upset by this indeed, does anyone else feel this way am i over reacting