I'm not going to be much help here, in my opinion cheddar should not do that (go sour)
I have had Caerphilly cheese in the fridge for over 2 months and not in sealed bags they just keep getting better.
I am thinking to much whey left from not pressing enough of course to big of cut on the curd or not cooking long enough will create the same problems,
and or not enough salt?
share your make notes then maybe some one can help you figure it out.
Now you need someone to chime in who can actually give you some good advice
Hang in there and keep trying, you will get better and more wonderful tasting cheeses will come along.