frozen you sound like me a couple of weeks ago, I spent all my time googling! DD is getting on ok but the gaviscon made her constipated which has not been fun
think I might stop it. There's been a big difference since she started the meds though, far less screaming (but still some).
FWIW, DD also had thrush fairly early on after I had antibiotics and it was quite obvious as she had little white patches on the inside of her cheeks. So I think you'd know if it was that? I may be wrong though.
I did spend a long time looking up lactose overload (which I think is an American concept but basically means foremilk/hind milk imbalance or oversupply) and I think my DD may have had a bit of that too. If you suspect your DD has it then I think colief would be good as it contains lactase to help digest the lactose. Plus there are lots of recommended breastfeeding techniques but you're probably following those anyway.
The things which tipped me off to silent reflux were a) DD developed a tiny persistent little cough (reminds me of pregnancy heartburn!) and b) I noticed that her crying was at its peak right after a feed and she would arch her back and c) I'd hear her swallowing when not feeding, then wait 5 seconds and she'd cry out 
All I know about dairy allergy is that it is pretty rare in breastfed babies, although it's more common amongst formula fed. Not sure how it works with mixed fed babies!
Hope that helps - it's so hard!
I'm thinking of giving up breastfeeding too. I am struggling with mega guilt and feel v selfish but I'm just not sure I want to do it anymore...