Hi M.,
Wow, 10 weeks and back to work--Yikes!
Did the tongue tie get fixed?
The rash is not affecting the milk, anymore than it's affecting any other part of your bloodstream or lymphatic system.
There are a number of causes of gassiness in breastfed babies, starting with 'some babies are gassy until their digestive systems mature' and all the way to 'I just couldn't eat broccoli ever without it being a major problem.'
There are a number of cures for gassiness in babies, from feeding them in a more upright position to carrying them in an upright position more than laying them on anything: human babies didn't used to lay down unless mom was laying down, and it's not really surprising that they don't do really well laying down for most of the day.
Some moms find that fennel tea (crush a tsp of fennel seeds and steep in boiling water for 5 minutes, strain and cool, feed a tsp or so at a time) helps.
Some moms finds plain water helps, particularly out of a small cup rather than a bottle.
Some moms find that they can't digest some foods very well themselves, and this inability is passed through their milk to their babies. While it initially feels like a hardship, giving up foods that disagree, it ends up giving moms more energy overall.
Some moms find that baby massage (google it, there's lots of free online source for 'how to') helps immediately.
In other words: try what you think is working, if it doesn't work, try something else you feel is likely. Trust your instincts is always a good way to go.