Where should i seek medical help for an ongoing spraining of my ankle?

Hi, of course there are several opinions to this enquiry, but what i would recommend is getting yourself an individualised rehabilitation program. As an Exercise Physiologist what i would do is functionally assess your movement to look at the ankle as well as the way the body moves as a whole. If there is a weak link in the chain then often an area will be sacrificed. True the ankle is probably weak, but what else is going on with the knees, hips, buttocks, back. How are they moving, what is tight, what is weak? The ESSA website (Exercise sports science Australia) has a ‘find an EP in your area’ link.
Good luck!

A physiotherapist, especially one in a sports clinic, can assess your ankle flexibility & strength then devise an appropriate treatment plan to regain  full painfree movement. They would also show you a home exercise program including stretching, strengthening & balance exercises.

I agree with Kylie, but feel a strength and rehabilitation program is significantly more likely to solve your problem by first treating the underlying joint issue. Then retraining strength, agiltiy and balance etc is much more beneficial.
Obvioulsy every injury is different but I would suspect an underlying ankle derganement (joint problem). 
I am a McKenzie specialised physiotherapist so would do a similar thing to Judi's suggestion but just from a different viewpoint I guess (there is more than one way to fix problems like this!). 
I would assess your ankle, and then determine a specific movement of the ankle which when repeated would likely clear the underlying joint issue up rapidly (within days to weeks only). 
Then I think the strength, balance etc can be implemented with much greater success.
When I hear of an ankle that has been a problem for years, I am almost certain of this underlying ankle derangement that needs to be sorted.

Weakness following an ankle injury can in some cases be related to a significant overstretching or rupture of the ligaments. If that is the case then it might also be necessary to see an orthopaedic surgeon as chronic instability may require surgical intervention. Usually a Physiotherapist will be able to provide advice as to whether that will be necessary or not based on the assessment that they will undertake during the initial treatment.

Weakness can also be as a result of a lack of strength or muscle control. Commonly an ankle sprain can involve damage to the nerves which help our body coordinate our movements as well as over-stretching or tearing of the ligaments and the tendons around the ankle. It's very important that full rehabilitation guided by a suitable health professional has taken place before people return to activities such as sports. The Physiotherapist in treating an ankle injury will look at a number of things including the need to restore full joint range of movement, as well as muscle strength, as well as coordination. In some cases taping or bracing might also be necessary to assist with recovery and initial return to activity but these will generally should not be considered as longer term options on their own.

Recurrent ankle stability is a common side affect of an ankle sprain that didnt get the proper attention it required when it first occured. Due to damging of ligaments during an ankle sprain, a combination of muscle wasting (loss of strength) and loss of joint control due to proproception loss. Another area to look at is your bodies overall balance and coordination especially with your eyes closed. Getting this addressed while you are younger is definely worth than having falls when your older and risk doing more damage (i.e. hip fracture). as mentioned above  to return stability to the joints a variety of techniques or approaches can be taken by a variety of practitioners, whether it be exercise physiologist, physiotherapist, or chirorpactic. They all will approach it differently as long as you get results. Just ensure that who ever you see that the work contains both strength work and joint stability.

Keeping this simple.
Your muscles on the side of your ankle (evertors) are probably weak.  You will need to strengthen them. 
You will also need some balance or proprioceptive exercises to stop yourself from these recurring injuries.
As Joel suggest, a McKenzie trained physio will be able to give you a tailored exercise program.