Kristina, Ive asked a friend here about Aubergines and your problem with them being bitter... Ive was told its the type you grow... maybe try a different one?
None of mine were, Ive often heard about them being bitter, but have never had that problem, Ive eaten mine raw chopped in a salad... they dont grow huge, I pck them early...
If you would like a packet of seed from here just let me know your address. Email me and I'll happily send you some..