Have you changed up your exercise routine lately? Variety often helps kickstart the metabolism.
I am down a foot in off my waistline, since I started 8 months ago. Was done mostly by adding different types of cardio twice a week.
I think the body just gets bored with the same old routine.
For the record I am not a Doc/physical trainer, run it by yours first and see what they think first.
"There are far, far better things ahead than any we leave behind" C.S. Lewis