8 week old struggle

Babies cry. We can't help that. But we just took our 8 week old baby camping, went super well.. She didn't get bit by bugs and she was happy all weekend. So we bring her home and she is the most unhappy baby ever which is super unlike her. I just thought it was a growth spurt because when I nurse her she seems to calm down for a while but this seems different than any of her other growth spurts. I had a friend say that it could be that my milk just isn't cutting it for filling her little belly anymore and I should try baby cereal severely watered down into almost a liquid... What should I do!?