I think that could absolutely be it. Concentrate less on the numbers and more on how you feel.
I don't weigh myself, and at the doc I tell them I don't want to know the number. They will tell me how much I've lost, though, if I have.
I go by fit of clothes and such. There will always be weight fluctuations anyway, and I would find that discouraging. Maybe weigh yourself less often, if you want the numbers. For me, the "number" is just depressing. I hated the "number" when I was in HS and fit as a fiddle, because I was an athlete, and not a petite little thing...whose numbers were so tiny!
Just some thoughts.
Oh, I don't have a clue what 600 grams equals in pounds.