Can i go swimming at a lake 2 days after my nexplanon was inserted?

Yes.: A Nexplanon insertion leaves a similar small needle skin wound that a blood test does. Provided the wound is healing well, and shows no signs of an infection (redness, warmth, discharge, excessive pain), you can keep the area covered with a bandaid while swimming, then clean the area with soap and water afterwards, pat area dry and reapply a clean bandaid.