I would certainly book an appointment with a physio.
In the meantime, as above, it really does sound like a shortened IT band. One very common, and often very effective, way to sort this is by using a roller, such as this one: £21 from SportsDirect. There are cheaper ones but be mindful that they may be too soft.
To use the roller put it on the floor and lie with your leg on top so that the effected side (this is the ‘outside’ of your thigh, so the left hand side of your left thigh and the right hand side of your right thigh) is in contact with the roller. You now need to roll the length of your thigh, from hip to knee, along the roller. You do this by moving your whole body. This will be VERY!! painful at first, but this will subside within the first week. 5 minutes a day is the recommended amount, you may find this hard to achieve at first due to the pain, that is ok. Stick with it! 🙂