There could be several reasons for a baby changing the sleep pattern
1)Growth Spurts:
Common times for growth spurts are during the first few days at home and around 7-10 days, 2-3 weeks, 4-6 weeks, 3 months, 4 months, 6 months and 9 months (more or less). the only thing you could do is nurse, nurse and nurse some more, it will last 1 week or so..
2)Teething
You can help soothe teething pain in a number of ways.
3)Seperation Anxiety, even the crisis age for most babies is between 12 to 18 months, some babies can show signs of separation anxiety as early as 4-6 months.
4)The diet change
So as long as the baby is not sick, you are fine.