Try Epsom salt on your plants.
A healthy growing tomato plant uses up lots of magnesium in the growing / production process. Maintaining the magnesium at the right levels can be accomplished with regular applications of Epsom salt. The results… more blooms, less blossom rot, more fruit, stronger plants, deeper green color, along with taster, sweeter tomatoes. Use 1 tablespoon to 1 gallon warm water (to help the salts dissolve).
Jan in VA