Which doctor should I consult and what diagnostic investigations do I need?

If you want your varicose veins treated, and definitely when you have acute symptoms in the leg, you should go to see your general practitioner or a vein specialist/phlebologist.
A phlebologist specialises in diseases of the veins and is concerned with the prevention, diagnosis, and treatment of varicose veins.

The diagnosis of varicose veins and spider veins these days is simple, non-invasive, and painless. At the start, the doctor will take your medical history. Then he will perform a physical examination by inspecting and palpating your legs while you are standing up. This will detect any varicose veins that are visible and any other changes in the legs.

For a precise diagnosis, an ultrasound examination of the legs by Doppler or duplex ultrasound scanning is necessary. Modern ultrasound devices are so accurate that they can provide an image of diseased sites in both the superficial vein system and the deep vein system. The type and extent of the varicose veins can be demonstrated in detail by ultrasound. This allows your doctor to draw up the optimal treatment plan for you.