Push-ups and weight lifting.....

I actually have a few questions. Recently I have started weight lifting/cardio training. My goal is primaly to build stregnth and to do better on annual physical fittness test that involve push-ups sit ups and a two mile run. Anyway my questions are...
Recently I haven't done as well as I should be doing on my push-ups and I was wondering if it is a direct result of my wieght lifting? (I have been excersicing those particulair muscle groups. Also keep in minf that it has only been a couple of days since my last workout I'm not sure if that is sufficient rest time.)
Also my forearms have been sore. It isn't really noticable but when I do push-ups or lift then it becomes painfully obvious. What should I do about this?
And finally any advice on how I can maximize my workouts and get the most I possibly can out of them would be greatly appreciated.