What is the next bra size up from a DD?

I gained some weight and it all went to my . I am in the process of losing the weight, but for now I need to get another bra. I am currently a 36DD but my s keep falling out of my bra. I know I'm not a 38 because that band is always too loose, so what cup size comes after DD? Is it DDD or E or something totally different? It really sucks because it's extremely hard to find a bra I like in a size DD so I'm sure it would be even harder to find it even bigger than that.