Dear mathilda: The first step would be a mammogram, if you did not already have one. Ultrasound is usually best at distinguishing a solid mass from a fluid filled cyst and may not be helpful in determining the source of your "dimple." If you have had a mammogram and it is negative, you might ask your doctor about a breast MRI. Another option is to gather a second opinion from a breast specialist. If all is negative, then early follow-up may be acceptable but a growing dimple needs explanation.
Mammogram would be the most important step: you didn't mention having it, although I find it hard to believe a surgeon would evaluate your for a new dimple and not order one, so I assume one was done and was ok. Ultrasound isn't all that helpful as a solitary screening device. If the exam and mammogram were ok, then followup is acceptable, although with a perceived change, I'd be inclined to make it more like 3 months than 6, initiallyl.
I had my last mammogram in May and everything was okay. Should I go ahead and have another one.
Given that there's a change in your breast, I'd be ordering another mammogram if you were seeing me: 7 months is a long enough time that it's possible something new would show.