Sounds like you're referring to Delayed Onset Muscle Soreness (DOMS).
If you're new(ish) to working legs at a that level, it will get better, but never go away. Eventually, you'll start lying and calling it "the good pain" as you struggle to get off the toilet.
For a first time injection, this video is is a bit dated and the host looks to be about 15 but if you can make it through, its actually a pretty good example of how to inject the quads.
https://www.youtube.com/watch?v=2PDqLDjMDtA
(This may be a bizarre 'first post' for someone to do but anyway...)
Where I live in the US I can buy them at a store that specializes in farming equipment and livestock animal care. they cost more, about 40-50 cents.... but its super simple. Not sure if that's helpful in Australia. Best of luck.