It’s not possible unless it’s defective.
The X has good quality battery suppliers. If you start at 100% / 0 cycles, you’ll reach 90% no sooner than 250-350 (avg 300 cycles or more). It’s very unlikely you consume even one cycle a day, leave alone 2+ per day. And even if you did consume 2+ cycles per day it would take 5-8 months to reach 90% that too if you’re unlucky.
For reference my X has a battery with 190+ cycles and I’m at 99% after some 6+ months or so.
Read again. You said March 2018. Then it’s perfectly normal.
You’ve had some 15 months so I guess 350-450 cycles already. So 90% is normal.