Lately I have been eating way too much and want to cut back, what can I do?

I'm by no means fat but I'm worried I'm hurting my body. I weigh 110-112 lbs. 5ft 3in and 17 years old. I eat a veggie at lunch and dinner and fruits at every meal. I rarely eat refined grains only whole grains and lean protein but I eat too much. My snacks are more like meals and I eat way too many sweets (ice cream, m&m's, cookies etc.) I want to stop eating so much and have portion control. I'm afraid if I continue eating like this I'll gain more unwanted weight and harm my insides. What are some step I can take to reduce my portions and refrain from eating more than I need. I also exercise most days but I'm putting on weight from all the extra calories!