hi,
thank you for providing the brief history of you.
A thorough musculoskeletal assessment is advised.
As mentioned ,that you were practicing for the run and feels like the digestive systems has some issue due to
hamstring pull than there is much less possibility for this.
Also, for run you need to balance your diet intake and your run output as well. Due to excessive loss of water during the run practice in the form of sweat and other
metabolism there may be a chance for the hard stools. For this I will advice to eat the fruits more to balance the fluid intake and output.
Now coming to your hamstring, if I has got a pull or a tear we need an assessment of the muscle to be performed. Also intially you have to stop training first as it will aggrevate the muscle fibres to not heal and later it may trouble more. Also, undergoing proper
physical therapy before training is advised to get the maximum output from the muscle.
I deal with sports cases regularly and prevention is better than cure for the longer runs. with physical therapy they respond well and perform better in a later stage of sports.
Regards
Jay Indravadan Patel