The doc may be treating you for infection but if there are no symptoms (swelling, temp, raised blood counters) he may be treating you speculatively.
I had "dull aches" down there about 18 months after surgery, I remember because I was skiing at the time and was convinced the tumour was growing back! It was probably the skiing!
4 years since diagnosis and the only pain I get now is from my arthritic hip.