different parts of your body are stronger. I am 5'4 and can lift crazy amounts of weight (squat 285, calf raise 500+, etc). Honestly, you need to lift more to get better at it. It isn't always about the most weight, technique is very important. If you want to bulk up, which doesn't necessarily mean more strength, eat lots of protein. In the off season try going through a lifting cycle: endurance (3 weeks), hypertrophy (3 weeks), max strength (3 weeks), and power (3 weeks). Weight lifting is one of those things that can't get better by doing something else, you have to just lift to get stronger, that is how anyone gets stronger for anything, let alone lifting. Hope this helps. 3 times a week is not that much. I lift 5 times a week, some people lift 6. on off days go for a light jog and work on plyometrics and balance (yoga/pilates). try this site:
http://www.sports-fitness-advisor.com/
good luck