Crashing during workouts

I've (F21) been going to the gym for around half a year at least consistently. I notice that in the beginning of the workout, everything feels fine. But around exercise number 3, I just crash? And what I mean is that my energy just drops. I always start my workouts with a warming up and I do split workouts 3x a week. This energy crash can be physical, mental or both at the same time. And sometimes it makes me feel sad, bored or sleepy even. It feels like I can literally just fall asleep.

This goes on and off because like I said on some days it starts around the third exercise and sometimes I get this crash after an hour of working out. But it just makes me feel so annoyed because of how drained I suddenly feel. I know you're not suppose to give up easily but it's messing with my progress during workouts. It's more than just "oh don't give up keep going" type of problem.

I try to rest between 2-3 min each set. I don't use any sport supplements, such as creatine, pre workout, elektrolytes or other things. I will be taking creatine soon when I have the money for it.

Do you have any advice for me or maybe the reason why this is happening? It would be nice if someone could help me with this problem. Please be nice about this. Thank you!