It is probably not your metabolism that needs boosting. You have probably hit the point where your body has adjusted to the deficit you have been in and the benefits of ketosis are dwindling which happens to most people when they get over 6 months of mostly being keto. I would suggest switching to something more sustainable such as calorie counting to make sure you are actually maintaining a deficit. It may also help to vary your amount of activity each day and possibly even the deficit you are in just so your body does not plateau soon.