1 1/2 year old throwing tantrums?

Whenever I go to pick up my son who is 1 1/2 from the babysitter, who is his grandma, he throws the biggest tantrum ever. He starts pulling his hair, throwing things at me, and when I try to pick him up he screams and scratches me.... Sometimes even bites. He loves being at grandmas as you can tell.. Is this normal? I feel like a terrible mom because my son doesn't even want to see me but would rather stay at grandmas. What am I doing wrong? Anyone else have this happen?