Feeling tired

Cristina • Cancer survivor (Hodgkin's lymphoma); hobbyist photographer/editor; Archaeology student at Johns Hopkins University; 22.
I've been feeling unnaturally tired for the past week. Not sleepy, per se. Just really blah. 
I'm about to be on my period, but I've never had this symptom before. 
I take levothyroxin regularly for my thyroid, so it can't be that. 
I've been in remission from chemotherapy for almost 4 months already, so that's unlikely. 
Could it just be this sleepy weather? It's super cloudy, rainy, cold, gets dark at 5pm...idk what else it could be.
 
Anybody have any ideas?