First of all, your weight does not reflect your fitness level, your body composition, or the type of workout you do. When you begin strength training, you will gain weight for several reasons.
With strength training, you may gain weight because your muscle mass is increasing and your level of body fat is decreasing. Muscle is always more dense than fat and takes up more space in your body. The change in the ratio of muscle and fat does not happen at once. It will appear you are gaining weight for the first couple of months before the ratio begins to change and it becomes noticeable.
When you begin strength training, you are putting stress on your muscle fibers. This stress causes micro tears and some inflammation and your body responds to this. When your muscles suffer micro tears, it causes the body to retain water which causes a weight gain. Your body is actually retaining fluid to help heal it. The changes are short lived. In addition, you may experience soreness in the next 24 to 36 hours.
The other reason for gaining weight has to do with the increased fueling of muscles. Your body converts glycogen or sugar to glucose which provides energy to your muscles. Glycogen has to bind with water as part of the process to fuel your muscles and when the body stores water, you appear to gain weight.
As your body becomes accustomed to exercise, your body requires less glycogen to produce the same amount of energy. At this point, your body will retain less water and you'll begin to lose weight and over a period of several weeks or months, you'll lose the initial weight you gained.
Although you will gain weight at the beginning, you will be able to lose weight over time. When you increase the amount of muscles in your body, you will burn more calories, thus losing body fat and eventually your weight will begin to decrease. It is strongly suggested that people ignore the numbers on the scale at the beginning since it is totally misleading. In fact, it is recommended people do not use scales at all.
The important thing to remember through this whole situation is that the volume of muscle takes up more space than the same volume of fat and muscle burns more calories than fat so you want to increase your muscle mass. Without a scale, you will notice the weight loss when you put on your clothing. Your jeans will fit better. Let me know what you think, I'd love to hear. Have a great day.