Thank you so much everyone for help, support and tips. At the moment i am working on a remote place so it might take a while to be able to see a doctor. I had these downs on energy often due to depression not long ago (and obviously depression is still set in...so it might affect the flow of stamina...or there is, as some said, something else...) and also temperatures are high here now, which has been something that also makes me more exhausted than mild/cooler temperatures.
Anyway i am going to try some of the ideas and advices you gave me. Thank you very much everyone