Activity after breast reduction
Congratulations on your recent surgery! Definitely talk with your surgeon about activity limitations as each surgeon has a slightly different protocol. I would not recommend something as vigorous as the hike you are describing this soon after surgery. Your body is still healing on the inside and too much activity can disrupt this. It won't be long though and it sounds like you are doing very well if you are wanting to go hiking already.
Light Hiking 3 weeks post op?
Congratulations on having undergone the breast reduction procedure; this operation tends to be one of the most patient pleasing operations we perform. Your plastic surgeon will be your best resource when it comes to returning to specific activity given that he/she knows how you are progressing and whether there have been any complications. Keep in mind, that most patients will not be at their full strength/family three weeks after breast surgery.
My suggestion to patients: resume activity gradually and listen to your bodies as you do so. Having said that, assuming you have had no complications, it is likely that you will be able to return to light hiking three weeks after surgery. Best wishes for an outcome that you will be very pleased with