Looks like nutrient deficiency. Are you feeding them regularly?

Yeah I actually fed them this morning, although I did not do it in the past, so that might be contributing to it.

The stuff I got said feed once a month, so I'm going to try that.

Tomatoes are heavy feeders and need lots of nutrients. You should have started feeding long ago (based on the size of the fruit in the background).
You should use some water soluble fertilizer with higher amount of potash (go for 15-15-19 or 19-19-25 or some similar N-P-K ratio) and with micronutrients (Ca, Mg...). You are dealing with multiple nutrient deficiencies and your plant needs them fast (water soluble fert nutrients are readily available to plant, so i'd strongly advise you to use those). Always follow directions for use on the label, over-feeding can hurt them too.

Good Luck,
Djole

Could also be watering stress, have they dried out to the wilting point recently? Perhaps been too wet for a period?