I'm with gillianl, I'd love to be at your weight and I'm only 5' --
That said, if you are gaining weight for no apparent reason, I'd suggest that you get tested for hypothyroidism, PCOS and/or insulin resistance. These are all medical conditions that can cause you to gain and/or be unable to lose weight.
Beyond that, I would suggest that you implement the food diary here on MH to track your calorie intake (includes food and drink). Then I'll suggest that you implement the exercise tracker to make sure you are burning as many calories as you think.
I know you are "young" yet, but keep in mind that as we get older, we do tend to "hang onto" extra pounds and if there is any problem with your metabolism, losing weight will be much harder than you used to find it.
i really don't see any problem with your weight in fact i would love to get to the weight you are at the moment, you are definitely not fat. All i would say is make sure you have a healthy meals a day and exercise the way you have been and the results will show, it's not going to happen overnight. Good luck