Before I started training for a marathon, I was a regular runner (obviously, lol), and I strength trained 3 days a week. Now that I'm running a lot more and harder, I'm nervous about getting injuries by strength training so often. I'm starting week 4 of 16 on my plan, and so far I've just been doing weights once a week, on my cross-training day. Does anyone have any recommendations about whether or not I should increase how often I lift weights, or what day(s) would be best?

(I'm using Runner's World's Rookie Marathon Training Plan...Mondays are cross training, Tuesdays are quality workouts, Wednesdays are easy and shorter, Thursdays are tempo runs, Fridays are rest, Saturdays are long runs, and Sundays are easy and shorter again.)