Nipple stimulation advice!!

This is my second baby and with the permission of my doctor I started nipple stimulating last night. I manually did it on each side for 15 min and not during contractions. The contractions started very quickly within 5 minutes I'd say and weren't unbearable but they were consistent so I had to stop several times because of contractions. So I only did about 15 min total really. Then the contractions lasted on their own for 2 hours until I was too tired to count and went to bed. They must have died off while I slept.

ANYWAYS ha. I lost my mucus plug yesterday afternoon and I have contractions that come once in a while and then leave. Do you think my body is ready? How can I get labor contractions going for real? How long do I stimulate until it's real labor?