Aw, understandable na worried ka, mama, babago talaga ang babies every month, pero sudden changes like that deserve a check with your pedia just to be sure everything's okay. A few of us mums noticed our babies had quiet phases din, sometimes dahil sa sleep regressions or just their personality shifting, pero around 3 months kung parang mas withdrawn siya compared sa dati, better safe than sorry talaga, maybe schedule a quick visit lang so your doc can rule out anything and give you peace of mind.