Any sport you take up seriously will bruise you up pretty badly for a while. As you get better and get technique down, there will be fewer of them. Just think of them as a mark of commitment. Or a badge of courage. And take tylenol, not aspirin- aspirin is blood thinning and will aggravate it all.
Get some bike porn, like Mountain Biker or Bicycling and read the articles on technique, or check a good bookstore for info. There are right and wrong ways to do things, and knowing them will save you some trail battering. Like"Where you look is where you go". Look at the way around the root and the bike will follow that line.
Acertain amount of getting smacked up is normal, but it gets old. Most us us learned things from magazines- don't underestimate it. And there's the cool stuff to buy ;D....

Lizzy