My advice:
-BE PUSHY.
-Look for another dr. if you're not getting answers from your current doctor.
-Don't let the lack of a diagnosis get you down.
-Don't let the lack of a diagnosis make you give up on trying to find the answers.
-Don't start to feel like 'it's all in your head' or it's 'really not that bad' just because doctors, or family, or friends, minimize your symptoms or don't want to hear about how you feel.
-Focus on what treatments and/or diets are making you feel better rather than what a doctor calls it. After 34 years of having everything from a 'nervous stomach', to a 'spastic colon', to IBS, to UC, to Crohns, to IBS, back to UC, to nothing at all, to Crohns, to UC again - well, you get the picture - I don't care anymore what they call it as long as they can give me medicines that help me feel better.
-BE PUSHY (oh, I said that - but it took me years to start being pushy with my doctors - something about that whole authority-thing...).
Good luck!