why am i like this with beer?!
Because that's the way proper beer is. Not only can it change from batch to batch but it changes as it matures in the cask - starting off slightly sweeter and slightly weaker than when it finishes. Plus, of course, proper beer is a relatively delicate product that needs proper and skilled care and attention. Bad storage can ruin the finest beer.
If you want a beer that always tastes the same then you need to find out beer that is stable - and that means sterile. Most commercial lagers are of this nature - one Carling will taste much the same as another Carling.
No source - I know about this from many years of personal research ;)
is it draft beer or in a bottle the only taste diff should be from draft, this would be because the different places have or have not cleaned their pipes or the beer its self may not be the same hooked the wrong barrel up to the tap. the pipes when cleaned have not been clean correctly still cleaning solution in pipes etc. could it even be the place is using rubbish beer? or beer from the drip trays believe me i've seen it all
The bad tasting stuff may have been old and past its prime.