Hmm... I highly doubt you were a 34D back then. On average most women's underbust is within 3 inches (plus or minus) of their waist so a 24" waist meant you probably had at the most a 27" underbust. That means you probably needed more like a 28F or 26FF (probably higher because a too big band can make cups appear like they fit when they don't). D cups are actually fairly small and most women need more like an F-GG cup if they're fitted properly.
Definitely get a properly fitting bra FIRST! There are actually a lot of good health reasons for this that I list here:
http://braslessinbrasil.blogspot.com...-to-teens.html (there are links to some studies there). But a well fitting bra can help to reduce back pain and if you're working out it's definitely a must! Also, you can actually damage your breast tissue if your wires are rubbing you incorrectly.
Also, if your bra is way, way off, you can take your measurements braless. Take your underbust first and then take three different measurements for your breasts:
1. Measure laying on your back around the fullest part of your bust including the nipples.
2. Measuring leaning over parallel to the ground around your entire bust, including the nipples
3. Lean over and measure around the perimeter of your larger breast including the nipples.
Then find the different from 1 and 2 and your underbust to get a rough estimate of your cup size (around the perimeter will also give you that same estimate but you don't need to subtract the underbust in that case

). Those three measurements should give you a good starting point on where to start when it comes to trying on bras.
If you're like mean and your breasts aren't as firm as they were when you were younger, it helps a lot to have a well-fitting bra! Otherwise you're definitely at risk for back pain and bad posture. Plus, it'll make a huge difference when it comes to the fit of clothes.
