I started my weight-loss program in September of 2015, after I gained 40 almost in 6 months due to a personal tragedy. I also have thyroid issue, so my doctor suggested that I try Phentermine with diet and exercise. I have started taking half a pill a day because it made me dizzy, my heart was beating too fast, and I was irritable plus constipated.
I stopped taking it for 2 month but at least maintained or i was losing 4-5 lbs and gained back when it was time for my period.

To make a long story short, I did lose about 20 lbs by taking half a pill a day,with 30 min of exercise, and portion control. I still struggle with picking healthier food, so I hit a plateau for the past month.
My doctor gave me a new prescription, so this time I started taking 2/3 of the pill to a pill a day. my irritability increased, and I still exercise but I appetite is like normal. I didn't have sweet-tooth before but now I do. Also, now I menstruate every 3 weeks so my appetite is uncontrollable during his time. I feel like taking phentermine just causes my period more irregular, my feet are swollen. But my weight stays about the same even with exercise and diet.
I would like to lose another 20 to back to my weight before, but I feel like this pill does not work anymore other than makes my period irregular, feet swollen, and worse other side effect.

Should I get off of this pill for some time, finish what's left before I go back to my doctor or should I keep taking it?

Could someone give me some advise please?