Should I see a physical therapist, massage therapist, or sports-medicine specialist?

I’m young, healthy, and relatively active. Until this year, however, my physical activity was mostly just lots of walking…But for my new years’ resolution I joined a gym and have spent the past year getting in shape. I run 3 miles three times a week and do other cardio (bike, stairs, etc). However, I feel like my body is still not adjusted to this major lifestyle change. Specifically, my knees seem to be rebelling against me, I get occaisional shin splints, etc. I’ll take a break from working out for a week and it gets better, but as soon as I go back to regular workouts the knee pain comes back, even with low-impact activities like biking. What kind of specialist could I consult? I’d like to make sure I’m excercising my muscles evenly, see what I can do to strengthen my knees, etc. The trainers at the gym are no help. Would a massage therapist know how to advise me? Or a different type of expert?