Gotta be careful which bar/pub you go to.
Just because you see Coors, Blue, Rickards, Stella etc. on tap doesn't necessarly mean that is what they are pouring you. You rarely see the keg because its usually in a big refridgerated room or under the counter of the bar. I've heard of stories that small establishments selling no name brand beer to unsuspecting customers. These are real shady places.
This will not happen is any big franchise bar, but you gotta watch out for the little booze cans or joe blows bar down the street.
Getting sick after 2 pints is soft man
No biggie, switch to bottles. The only thing I can think of is if the bar is not cleanning the taps/spouts out daily.