First thing is to stop bowling now, really STOP. get to a good local sports Physio who does get involved in cricket. This is a very common problem in young fast bowlers and has ruined many a career. I'll dig up an article on this and past it into this post shortly. But you need a thorough investigation and a very well structure and planned approach to your rehab.
Here's a useful article to take to the physio when you see them. Perhaps have a read yourself
Lumbar Spondylolysis in Young Fast Bowlers
by Caryl Becker, MCSP
Login and click on the attachment below to open the full pdf version of this article
Date written: Oct 2006 Published in:
sportEX medicine
Intro begins: A study by Hollenberg (1) showed that in up to 47% of adolescents with lower back pain, a pars interarticularis fracture was reported. In another study by Gregory et al (2) it was reported that the incidence of injuries in young fast bowlers was 0.165/1000 balls bowled, in comparison with 0.066/1000 in spin bowlers. In the fast bowling group, 17.6% of these were lower back injuries.