Help! My tomatoes have something... but I dunno what

[KathyDC]

Okay, it was bound to happen... especially in the humid climate where I live, and with all the ridiculous off-and-on rain we've gotten the past few weeks.

Some of my tomatoes are starting to get the dreaded bottom leaf yellowing. I can't quite decide what it is, though, so I'm hoping y'all can help. Any idea what it is, and suggestions for how to combat it are welcome. (I'm not treating them with any anti-fungals or anti-bacterials.)

I'm attaching photos of my Dingwall Scotty plant, which are fairly similar to what I'm seeing in some of the other plants.

Front of affected leaf - Back of affected leaf - Other leaves showing yellowing on the same plant

And to make myself feel better, a shot of the fruit it's putting out anyway!

Thanks for the help,
Kathy