Bra advice? Please bra wearing ppl only!?

You're not fat at all! ALL bras are different! For me, La Senza makes me have to buy bigger bras whereas, if I go to M&S, I can get a 34C or a 32D and both seem to fit. Don't panic. You need your bra to fit properly. However, I recently bought a bra that was a B. Usually, the bigger the back, the bigger the cup. You can get a B with a small back and an A with a bigger back and the A can often have a larger cup size. Find a bra size that most suits you. Mine is 32D but I always buy different sizes depending on style/place of purchase. The best way to discover your general bra size is, as awkward as it may sound, to get a fitting! You stand in your bra and they just take a few measurements to ensure you get the right size.