Why do I have different shaped ears? Is this common? (photos)

It is actually not “normal” to be perfectly symmetric between the left and right side of your body. Some kind of asymmetry, whether in size or shape, is the norm. So, to have two different sized/shaped ears is totally normal. If this bothers you, you can consider ear surgery to correct the flatness of your left ear. It looks like you have Stahl’s bar, in which there is a vertical bump in the upper portion of your ear that flattens out the curved part and makes it a little pointy.

No ones facial features are completely symmetrical. From your photos it looks like the folds on your left side are a underdeveloped compared to your right. IF desired this is easily correctable with a daycare surgery under local anesthesia
I suggest you meet a qualified cosmetic plastic surgeon who can resolve your issues

Nobody is perfectly symmetric.  Your ears are sisters, not twins.  There is a certain amount of asymmetry that would thus be considered a variation of normal.
From the pictures, it appears that the left helix is underdeveloped from about the 1-4 o'clock position.  However your right ear also does not appear to have a super well developed helix.  So in this sense, the helix on your left ear is just a little less prominent that on the right side.
Its hard to understand the three dimensional orientation of the ears from just the pictures.  I can guess (but you deserve better), so for a specific opinion on your case, please seek an in personal evaluation with a plastic surgeon.
Best of luck!