Implants which are submuscular (under the muscle) tend to involve more discomfort than those that are placed subglandular (over the muscle). This is related to the stretching of the muscle of the implant and also the movement of the muscle with normal activities of daily living.
Different surgeons view the use of non steroidal anti-inflammatory medicines differently, but I think they have a role is helping with this discomfort in the weeks after surgery. The key thing is that the pain should be improving with time. If the pain is worsening, you should go back to see your Plastic Surgeon to make sure everything is ok.