Resolved Question: I'm eating well, exercising regularly yet somehow getting fatter?

I eat relatively healthy, and exercise about 3-5 days a week, depending on the week, yet somehow my jeans aren't fitting me anymore.
On a typical day I would consume the following:
Breakfast - fruit smoothie, or freshly squeezed juice, coffee/ oolong tea
Morning snack - small bag of peeled/chopped apples + green tea with honey and skim milk
Lunch - whole wheat tortilla with vegetables and humus
Afternoon snacks - small bag of chopped carrots/peppers + small bag of pineapple
Dinner - baked fish with vegetables
I generally don't eat after 7-8pm

My exercise routine consists of 15-20min on the treadmill, half an hour of weights - low to midsized, with high reps, and 10min of stretching and abs.
I never weigh myself, since it tends to become an obsessive and mentally destructive habit, but my jeans, and belts speak for themselves. I'm in my mid-twenties and generally not overweight, but more so slightly soft around the edges. How is it that despite my diet and exercise, I'm gaining weight?