Tantrums already!

My baby thinks he's two! He's not even a year old yet (still 2 weeks until his first birthday) and he's already throwing tantrums. Any time I tell him 'no', or confiscate something he shouldn't be playing with, he bursts into tears and throws himself to the ground! At the moment we're thinking that the best course of action is to ignore him when he does it until he calms down, but it's not making any difference.

He's been very moody recently and we can't figure out why. I only have 2 theories as to what could be causing it.

1. maybe he's teething and not feeling his best, but he hasn't reacted like this before when teething
2. some sort of separation anxiety. He has stayed over at his gran's a couple of nights recently. He never takes this well, and keeps his grandparents up all night. The first night he stayed he went on a hunger strike in the morning and wouldn't eat his breakfast. He wouldn't even take a breastfeed when i went to pick him up in the morning and refused to take his breast milk until we were back home. He also 'punishes' me for a couple of days afterwards by being grumpy and clingy and bawling every time i leave the room.

Can anyone suggest anything we can do to stop this behaviour in its tracks?! He's usually such a lovely baby, but at the moment he's behaving like a stroppy teenager and it's really getting me down!