I have pain in my middle/lower back. Please suggest?

Please take rest whenever required. Do not overexert yourself anytime during the practice and do as much as you comfortably can. You can also practice this flow for back pain relief: https://www.youtube.com/watch?v=1iuRqY7eYkI 

 As we are not medical experts, it is best to take Doctor's guidance on medications and diet to be followed.