I'm not a physio but it sounds like you have shoulder instability in the right shoulder. I'd suggest that you go and see a physio to see if they can diagnose what's going on. They will also be able to suggest what exercises you should be doing and a graded program to help get your strength up.

You may be noticing that one of the reasons why you are not getting stronger is that you are strengthening your shoulder in a different range. There are some great shoulder physio's around in Sydney. The guys out at the North Sydney sports medicine and physiotherapy clinic are awesome. There is also another place which is in Sydney called the shoulder injury clinic.