Try this shampoo:
Alpecin Caffeine Shampoo C1, Hair Loss Treatment, Hair Loss Product
I shoplifted this from Boots the other week, apparently the caffeine is supposed to stimulate the hair follicles if you leave the shampoo on for several minutes before rinsing. I got it to see if it lives up to the hype, even though I don't have any hair loss, I just wanted to see if topical caffeine stimulated my hair and scalp. I tried it out and it definitely does! I would totally recommend this shampoo as well if you're hungover, a few minutes on the scalp and it helps bring you back to the land of the living.
As other people have said, get a hair MOT and if you feel your GP isn't being the font of all knowledge in respect of all things follicular, insist on a referral to a trichologist.
EDIT: The kelp thingy. YES. I've taken kelp supplements without fail for the best part of 20 years. I still have a full head of hair which I attribute to genetics (probably the only legacy my parents gave to me that didn't require addressing in therapy) but still, all the colouring, chemical and heat styling I had over the years should have rendered me bald, I attribute the good condition of my hair to kelp.