What do I do ?

I've noticed over the last couple days that he is getting more and more aggressive. He has bitten me twice. Not nipping , biting!
Last night for instance, he was begging for ice cream from my BF and when I old him to get off the bed, he bit at my leg, the only thing between his teethh and my leg was the blanket. Then this morning when I took him out for his run, he ran at me twice, which isnt out of the ordinary, usually he just runs by me, this time he ran and jump on me then he ran and jumped on me again and this time growled and bite my arm, luckily I was protected by my sweatshirt. he didnt break the skin, but I will have a bruise. He is approximately 1 year and 8 months old. Very active, and we let him run all the time, we have a big yard, both front and back.
I have instructed the little ones to not get into his face or play with him right now, because he must be going through something. Is this behavior normal for this type of dog ( Boxer/mastiff) and for his age, what types of things can I do to help him through this with out becoming totally aggressive???

PLEASE HELP !
Thank You
Amy-Elizabeth