I usually get strong cramps and muscle pain after training the next days. I take whey protein every day one shake, but the pain is there – do I need anohter whey protein, or some other supplement?
If it's DOMS that you are getting (delayed onset muscle soreness).
Beta-Alinine is very useful for this.
But if it's Muscle Cramps.
Then it could be a couple of things.
Dehydration/Magnesium Deficiency/or Electrolyte Imbalance from Fluid Loss.
So make sure that you are Hydrating Properly, especially in this Heat.
Then adding a Magnesium Supplement is Beneficial, since most people are Magnesium Deficient.
And Magnesium is responsible for Proper Muscle Contraction, along with over 300 other Enzymatic Functions.
I take 400 Mg of Chelated Magnesium (Chelated ~ means bound to an amino acid for better absorption).
Another product you could add if it's Muscle Cramps is an Electrolyte Liquid.
I use 40,000 Volts Electrolyte Concentrate from Trace Minerals.
It combines "Concentrace" Trace Minerals and Utah Sea Minerals in a base of Potassium Chloride.................. JP
P.S.
Here's a little article on the Benefits of Magnesium, of which about 80% of the Population is Deficient.
http://www.ancient-minerals.com/magnesium-benefits/