Hi,
Changing timezones make no difference at all to your milk supply. Our bodies respond to our baby's demands - not the clock. Siple recipe - the emptier your breasts are the more milk they make.
You will find, however, that the timezones mess with our bodies. It's common to feel jetlagged and out of sorts when you arrive in a new timezone. Babies often seek comfort at the breast in the form of more frequent feeds to help get over this stress. Doesn't mean you aren't producing enough milk - just that you are a bit out of sorts.
Get yourselves, including your little one, out into the sunshine - this helps reset our body clocks.
Re the sore nipples - take care with positioning and attachment. It may be easier now you are home, and without the recent distractions. YOur baby's age makes no difference to his sucking - breastfeeding is not meant to hurt