new to this site I think its great! Well I have been boxing/kickboxing for the past 6 yrs and when I started I definitely had elbow soreness. I can say that is sounds like overextending the arm as well especially if its your non dominant hand! 2 days rest and icing helps a lot. Also, be watchful of your knees while pivoting, another mistake I did in my early days. I would let my knee lag behind at the pivot point during shadow boxing and target/heavy bag work and my right knee was sore for about 3 weeks! Minor mistakes we all have made as beginners.

I have been boxing/kickboxing for the past 6 years and when I started I definitely had elbow soreness. It sounds like overextending the arm as well especially if its your non dominant hand! Two days rest and icing helps a lot. 

Also, be watchful of your knees while pivoting, another mistake I did in my early days. I would let my knee lag behind at the pivot point during shadow boxing and target/heavy bag work and my right knee was sore for about 3 weeks! Minor mistakes we all have made as beginners.