Hello, i know this thread is quite old now but, i have the same problem.
Started to feel sluggish about two years ago, used to run daily at around 8.30-9.00 pace and felt great. Now chug along about 11 mins per mile and and drained if i run further than 5 miles.
I had a scan yesterday which revealed i have two large fibroids and a cluster of smaller ones.
Im relieved that i know what's wrong now. But have to wait to see consultant to find out my treatment.
Im writing this whilst sat in my running gear about to go for a 3 mile slow job.
Im only 37, bit fed up.
x