Pregnancy Test Negative.Delayed Menstrual Cycle,tiredness.Cause?

Hi there
Im 23 yr old female and i have missed my periods (1week late now)
I have taken 2 pregnancy tests and they have been negative. I have also noticed hairloss, going through stints of eating heaps then having no appetite, gained 3kg (even though diet hasnt changed) Feeling tired and wanting to sleep al the time.

Please help me