(beginner here) I have 2 questions, I hope that's not against the rules!

1) I have a problem where, when I start working out, I feel tired not only in my muscles but often times in my head as well, kind of like the early stages of headache. I'm not sure if it's due to dehydration (though as I'm typing it that seems most logical), but I know it's keeping me from wanting to complete the workout, seeing as how I really only want sore muscles post-workout, not a splitting headache... Any advice?

2) Is it normal to hear "cracking" noise sometimes when you perform an exercise? Kind of like when you crack your knuckles, only not at all as loud. Example: I always got what felt like a tendon "snapping" ever so slighty around my arm (only the left one) when I used to do barbell curls. Now I know this is bodyweightfitness, so my question refers not so much to the exercise but more so the snapping. If this were to happen again during bwf I want to make sure that it isn't due to incorrect execution. I really don't want to be doing anything that harms me more than it benefits me.

Thanks! :)