I had a real problem last year with "Blossom End Rot." The fruit rots from the blossom end. What a creative name.
Apparently, it's a lack of calcium. When they grow fruits, they need rather a lot of it.
So I supplement the soil with crushed eggshells. I roast them first, to kill any nasty bugs, and to keep the smell under control.
Then I crush them with a potato masher, and mix it in with the soil that I plant peppers and tomatoes in.
Bone meal is also supposed to help. But it takes longer to metabolize.
Well, we'll see how it works.