I don't know how long you have been exercising, but if you have sore muscles, our muscles tear during exercise. Then water replaces it to help the muscles heal. This can lead to a gain on the scale, but it isn't a true gain. This could be a reason for the gain. Plus, sometimes we lose fat, but not pounds when we exercise a lot. My friend didn't lose a pound for months, but went down 4 sizes. You also build muscles which is much leaner than fat, so you end up going down sizes. Try not to focus on the scale as much. Make sure you are eating enough to fuel your workouts. Eventually the scale will catch up. Think of it this way, would you rathr be a 150 and size 2 or a 150 and a size 6 (just an example). Exercise can make all the difference. You are doing great. Just keep going and drink some extra water.