My recent physical revealed low blood platelets (131, 000). Pc wants to redo labs to be sure. If they're low, what could be the reason? Worried!

Low platelet count. Your number is just outside of normal. It is very reasonable just to repeat. There are lots of causes but no need to worry if normal on repeat.
Lab error or real. Most physicians would not consider a platelet count low at 130k although most labs list 150-300k as their norm. The platelets are fragile & subject to clumping in the specimen& that drops the count. Repeating a level would be prudent. True low counts come from decreased production or increased loss/destruction.I'd have your count repeated .