I am not sure - could be digestion issue, the way your body processes the fructose in the fruit, etc. It is not a sign of an allergic reaction for sure so you can still continue to consume it. If it makes you too uncomfortable then switching to other fruits is also an option.

You may intolerant to fructose. Or, it may just be that consuming excess liquids gives you loose stools. You are unlikely to be allergic.