The weight work seems to have got your body out of balance. Not uncommon, and the weight gain is not helpful. If you must do gym work, don't do heavy weights. people in gyms fail to understand that not everyone is a "body builder" type. Add the heavy work to things like protein supplements (and nothing else!) and the result is bulk. Useless for cycling. These methods just build up bulky heavy muscles. Use light weights and multiple reps. This tends to create strength and, more importantly, endurance. My own winter routine in race days (years ago!) was twice a week circuit training, runs, very light weights, and about 250km a week steady riding, before proper training started in late November. Never gained a gram of weight, in fact some winters it came down a little, all to the good. Keep away from heavy weights, lose the weight, and chances are the pain won't come back.