What, if anything, is unbalanced about this homebrew College of the Storm bard subclass?
I think the subclass I made is unbalanced because of the number of abilities gained at third level, and the combo moves you can pull off with Stormy Blades plus something like thunderous smite - but I am not sure how to balance it while keeping the feel of this subclass.
College of the Storm
Bards of the College of the Storm use the creative magic of thunder and lightning. They bask in the beauty of the storm.
You gain proficiency with medium armor.
When you join the College of Storm at 3rd level, you gain the ability to make your weapon attacks magically imbued with thunderous energy.
Once per short rest when you hit a creature with a weapon attack, you can choose to deal an extra 1d6 lightning damage to that target. This damage increases when you reach certain levels in this class, increasing to 2d6 at 5th level, 4d6 at 10th level, and 7d6 at 15th level.
In addition, when you join this college at third level, you learn the thaumaturgy cantrip, and one additional spell from any class that deals lightning or thunder damage the spell must be of a level you can cast. When you choose this spell, it becomes a bard spell for you. If you choose to replace this spell when you gain bard levels, you must replace it with a spell that deals lightning or thunder damage.
At 6th level, you may attack twice, instead of once, whenever you take the Attack action on your turn.
Starting at 14th level, when you are hit by a melee attack, you can use your reaction to deal lightning damage to the attacker. The damage equals your bard level. The attacker must also make a Strength saving throw against your spell save DC. On a failed save, the attacker is pushed in a straight line up to 20 feet away from you.