Am I meditating correctly?

How do I know if I am meditating right? Initially I used to sit without any support and medidate. But due to back pain I started taking support of the wall. Now, with the support I feel like I sleep for 40-50% of the duration. (due to the added comfort I guess) I start with taking deep breaths, around 12-15 breaths. Post that I try to start concentrating on my breathing. Some random thoughts start coming to my mind and I try to bring my mind back. Sometimes I feel I am blank, no thoughts, and neither the concentration on my breadth. I neither feel that good, nor do I feel bad after meditation. Am I doing it right? If not, what am I doing wrong?

PS: I have been medidating from past 15 days.