Update: I think my D Cup bra is actually too tight on me, I could probably afford to go up another size.
I also had an experience yesterday that was interesting... I wore one of my dresses from about a year or two ago when I last wore it, it was on the tighter side even when I used to wear it. Getting it on was enough of a struggle, it got stuck where my chest started. I found this pretty funny and kind of validating. Despite my best judgements I pulled and pulled until I was wearing it.
Later on I had to take it off and thats where the real problem started. I couldn't pull it back up OVER my boobs. I even managed to slip my bra off underneath and still no luck. I was completely stuck in this dress and I had to cut it off in the end.
Although I had to ruin a dress I loved, this was a really validating experience for me in a lot of ways. Very solid proof that my boobs had grown since I used to wear that dress all of the time (and I used to take it off WITH the bra on). After I took my bra off, the dress even looked great without a bra and with some cute side boob which is something I NEVER thought I could accomplish.
Just thought I'd share the story 