If you are doing exercise for the first time, then that kind of issues are happen. You have to gather some information about exercise from the professional trainer or doctor.
Would see a Gastroenterologist. Rarely there is a condition with a lot of "blood shunting" from the GI tract.
Besides the fluids what exercises did you do and how many reps and sets did you do?? During your exercise routine are you breathing correctly? whatever routines you do make sure to warm up before you do the exercise. An example would be lets say you're doing arm curls and you're curling 15lbs
to warm up do a few sets using 5lb weights so you warm the muscle up!
Be careful with you exercising you're 14 years old and still growing.
Avoid strength training on consecutive days, and finish each workout within 40 minutes. Target two or three muscle groups during each workout session. For example, a workout to tone the body might target leg muscles one day, chest and back muscles on a separate day and arm and shoulder muscles on a third day. Perform two or three exercises for each muscle group. Start with bodyweight exercises, such as situps, pushups and pullups. Then progress to basic weightlifting exercises, such as bench presses, lat pulldowns and squats.
drink water before in the middle and after ur work out and make sure you start with something Easier then get harder hope that will help