Weight Gain

Hi

Can someone please help me figure out why I have been consistently gaining weight? I only have about 5 lbs to lose but this past year I have gained about 10 lbs. My ideal weight is 105 (I am 5'1) and my body is currently at 110. I realize before I was underweight and didn't have enough muscle but I would really like to get back to my toned 105 lbs. I am a runner, I spin 2x/week and I am lifting 2-3 times per week. I have a consistent yoga practice and do pilates. Once there is snow, I also ski on the weekends - I generally mix up these workouts and do something 4-6 days per week.

My diet is not perfect, but fairly good. My sugar intake is usually too high (I like dark chocolate :) ).

Any insight would be greatly appreciated. Thank you!!