Zoloft and mg dosage

I've been on Zoloft for about 6 months now. I started at 50mg a day and I am now at 100 mg a day for anxiety. I think it really helps me a lot. I haven't had a panic attack since I started taking the 100 mg dosage. For the first few days of both dosages I felt jittery and my pupils dilated. After that, though, nothing really has happened. I weigh 122 lbs and I am 5'4, so I don't know what it is. My doctor told me that the higher dosages are usually perscribed to people who have anxiety, while the lower dosages are given for depression. I haven't gained any weight, and in fact I am loosing weight. All in all, I think it is a very helpful drug.