I have had a clematis for years. I don't know what it is. It was given to me by a friend. It is a pale lavender. The first several years it bloomed wonderful, then the last several years it has hardly bloomed at all. I've pruned in down in the spring, then I've not pruned it in the spring and nothing is working. I fertilize with a all purpose time released fertilizer and then miracle grow. Nothing has helped. It has great leaves and is very full. What am I doing wrong?