ivana, that doesn't sound right, usually after the initial few days of lousiness people feel very bright and full of energy. are you generally well otherwise? i would suggest seeing your GP as it's possible you could have an underlying health problem (don't want to worry you, sorry).
what are you eating? are you eating enough, and eating enough fat, and getting enough fluids?
I am on day 6 now and had terrible headaches for the first 3 days that has now gone but I still have the tiredness, not been able to exercise as so tiredness, I have heard a little about ketosis but from stories I have read that usually kicks in after 2-3 days.