I increased my levels however I notice sales falls as the gig popularity goes down, I mostly rely on buyer’s request area to get orders
Your gig popularity will fluctuate over time. Fiverr rotates all gigs around in order to keep the site fair for all sellers. Nothing to worry about, it’s quite normal for sales to go up and down.
Actually only new sellers are rotated. Usually from Level 2 you can say goodbye to new sales, because it’s considered that you should get sales from your existing customers. This trend was implemented from Fiverr 3.0 release, who ruinned the sales of almost all Level 2 sellers (and some TRS).