Are there any safe dietary supplements for weight loss?

I worked hard without dieting for about 2 yrs. and lost about 25 libs. recently (since Dec) when I went to the doctor I had gained 18 LBS!!! I have been sick and not going to the gym as often, but I still go 3 to 4 times a week. Not as much cardio because my knees and feeet had been bothering me. I do Body Pump which is strength training, but I don't know what to do and I am so depressed. I was already buying clothes a bit smaller and now everything fits snug. Any suggestions? Need a