I know this has already been said, but I think it is very important for you to realize that lifting five days a week is hurting (not helping) your ability to put on muscle. You need to do full body workouts three times a week. This alone (before I even began to learn about proper nutrition) allowed me to put on about 5-10 pounds of muscle when combined with Grow! shakes. Make sure you are getting a shake post-workout, both after running and lifting.
Just FYI I am also 5'8", weighed 120 lbs. when I graduated from HS, and 135 lbs. when I graduated from college (running cross country and track throughout). I looked a lot more healthy at 135 and it didn't hurt my times at all. However, I also just did some natural "filling out". If I had put that much weight on too quickly I surely would have seen my times suffer.
I have been out of school now for about a year and a half, working out seriously and getting proper nutrition for the last six months, and I now weigh about 160lbs and have gained a lot of strength. Even though my body was capable, I never could have put on this weight while running, hence my comment about conflicting goals.
FYI, some of the coaches on here probably have some experience with athletes that want to put on some size/strength without gaining a lot of weight.