I don't know what specific kind of cheese you are making and if you are intended acidification to continue in the fridge and even what "sour" and "bitter" mean to you. So, all that said
, if your cheese is "done" when it goes in the fridge, it sounds to me like your storage temp is too warm. Again, it really really (really) depends on the kind of cheese you are making, and I am assuming it is a basic lactic with no rind that does not have a hastening phase, but might want to at least get it under 8C/46F and really think about 3-4C as the target storage temp.
PS- if you are using vegetarian rennet, it can sometimes result in a slightly bitter taste in fresh cheeses...
Not sure this helps at all, but good luck!