Boobs are growing without any reason

So, I'm in my late 20s. In the past couple of years my boobs grew from 34B to 34D and they're still growing. I've no clue why this is going on. I'm not on any birth control, never have been either. No weight gain, still fit the same pants. Definitely not pregnant. I got a bit scared about breast cancer, so keep checking for lumps; haven't found any yet. Anyone has any clue why this is going on? Should I get them checked? Any advice is welcome. I'm a bit worried at this point.