Hello again!
I have done some more research and found out what it is I have done to myself (I think, waiting for my physio appointment on Tuesday). 🙂
The name of the syndrome is Piriformis Syndrome and is a result of this short muscle putting pressure on my sciatic nerve. There is a very good article here.
Cheers guys! Look after your Piriformis! It is a pain in the ass to have what I have. 😀