+ a load for that. It's more like riding a horse - rise with the bumps. You wouldn't sit on a galloping horse like a sack of coal and a bike has much the same idea of suspension.
Tyre pressures are simple enough bigger = lower [usually] MTB at around 70 touring 80 - 90 and race 100 up [others might disagree but the above works for me]
Remember you're not on a trials m/cycle with 8 - 10ins of suspension travel.
As for taking it back to
Halfords unless there is a clear fault then why ? Tyre pressures, saddle, riding style are all down to you I'm afraid