I would make sure you have the right seat height, and a proper width saddle for your riding position. General rule of thumb is the more upright your position, the wider your saddle can be.
I've noticed that, for me, the combo of cotton and summer heat makes for trouble in the "saddle regions." I wear UnderArmor boxer briefs under normal clothes and find that works extremely well in all conditions. They are pretty much like bike shorts but without the padding, so you can wear them all day off the bike, walk in them, etc too.