Weight Loss Plateau

I’ve been trying to lose weight ever since February and I can’t seem to lose much. I’m always between 165-155 and I can’t go above or below. I’ve been watching what I eat and eating less than 2000 calories a day and I go to the gym twice a week. What am I doing wrong? I’m trying my absolute hardest, but it’s not good enough apparently. I do have my slip ups and eat unhealthy or fast food. but it’s not that often. The worst thing I still do is drink diet sodqs.