Hi Lampy
Have you been involved with any other sports?
Also have you had recurrent hamstring strains/tears (even if they were minimal)?
The reason why I ask is because scar tissues and knots/trigger points may feel very similar.
Either way it is important to stretch out your posterior chain (ham, gluts, calves, lower back muscles) AND work on strengthening tailored to suit your sport/activity.
I would like to see how you progress.
Kind Regards
Jonathan