It is considered a physiology rather than a disease. The normal breast glands seem to get stimulated by your hormones. It goes away after menopause. Perhaps genetic, certainly environmental factors such as food ingestion, fats, caffeine, chocolate etc make it worse. The steps you've started should get rid of the tenderness.
Caffeine is especially bad.
If after 3 months those dietary changes haven't improved the pain, you might severely cut the fats in your diet, even go vegetarian for about 3 months. Most of the time, fibrocystic breast changes are decreased on birth control pills. Sometimes, however, I've seen certain progestins in different pills make it worse. There are conflicting studies on this as you can see from the abstracts below. Often progesterone is cited as the culprit probably because breast tenderness is a symptom of the luteal phase when both hormones are present in higher levels.