failing to lose weight?

I've been on phentermine for about 3 months and I'm SO sick of being stuck at 153-157 lbs. I have been fluctuating between those weights for about a year which is why I was put on phentermine in the first place because I was not losing weight despite regularly working out.

I am in a caloric deficit. I eat about 1200 calories a day on average. I have considered eating less than what I am currently but I do need to eat to keep up my energy levels otherwise eating less than this causes headaches and I lose focus (important since I'm a graduate student in my final semester).

Does anyone have suggestions on anything I could switch up or try? I've considered adding in intermittent fasting to this mix but I am not sure.