For the past couple of weeks, the skin on the outside of my left thigh has gone numb. i am not sure as to why this is happening, the only thing i have changed about my lifestyle recently is being sexually active again. should i be concerned?

YOUR BODY IS TALKING TO YOU! Listen & take good notes. When does it start/stop? Where does it go? What makes it better/worse? How long does it last? Medication helps/worsens? 
If you think it is something you eat/drink/do stop it & see. If better, go back again & retest until u r convinced it is something u should stop. Then stop it. Discuss with your Drs. You all will figure it out.

Follow up with neurology. May need MRI of lumbar spine and pelvis as may be due to disc/sciatica or can be ilioinguinal nerve impingement or lateral femoral cutaneous nerve impingement ( especially if overweight) . https://www.healthline.com/human-body-maps/lateral-femoral-cutaneous-nerve#1