Im looking for tips to stop my pup, Billy from jumping and biting which at times (mostly evening) gets out of hand and nothing seems to stop him. He has ripped clothes and hangs off my leg, jumps and bites my bottom which hurts! To attempt to ignore him is impossible as his bite hurts too much, he usaully chooses a time when I am exhausted and wish to sit down peacefully and watch TV!

First, Welcome to K9Academy ...

At 12 wks, most puppies use thier mouth to learn about the world and dont realize that they are hurting you.

More, and longer, play sessions combined with you telling the pup that he's hurting you should help. The way you communicate with Billy is to "shreek" when he makes contact. A VERY high pitch "Owww" or a squeel will let him know that he's hurting you. This is how dogs communicate with each other.

Jumping is a bit different ... Jumping is thier way of getting attention. When he jumps on you, you need to turn around, move away and ignore him COMPLETELY until he stops. When he stops, give a treat or a tactal reward and praise for staying down.

I've just been through this same experience. I have an almost 7 month old Rottie pup that went into play frenzies, especially in the evening, and it was pretty much like having an overtired child. Nothing consistantly got through to him that he needed to slow down. Playing fetch in the yard was good, but if the phone rang and I actually attempted to talk to anyone on it, he would start nipping at my clothing, shredding it. He wanted my attention and right now! Hang in there. They do eventually learn. Ignore bad behavior and if he gets too rough cross your arms and stomp out of the room. Put a door between the two of you for a minute or two. By doing that, you just took away what he wants most and he'll start to think about it when it happens a time or two.
I also took Baloo someplace new every day. Good mental stimulation in addition to physical.
We went to a puppy socialization class, for walks, to parks, through car washes, to Petco, etc.

Hey there! welcome aboard!
your dog is still really young and needs to be trained and he will soon understand he is hurting you and that is unnaceptable behavior. just give it some time, patience, and teach him. good luck! hope it gets better! (it should )

Yes, a warm welcome K9Academy!

And I agree with everything that has been said above. Its going to take lots of consistency though, and make sure that you aren't rewarding the behavior is any shape, way or form. Sometimes even by pushing off a dog, they might interpret that as play. So ignoring (although it seem impossible) is the first step.

Next step would be to redirect the behavior, such as in turning the biting session into an obedience trick session.

But overall your pooch may need some more mental and physical stimulation. Here's a list of games I compiled that you can play with your dog to tire him out: http://k9domain.org/games.aspx

Hope it helps!