Colic by definition is more than three hours of crying per day, for more than three days a week, for more than three weeks. Researchers actually don't know the root cause however there are many working theories. Find more about Colic in Babies and its remedies.
At 7 months of age, your baby needs 11 hours of overnight sleep and 2-3 hours of daytime naps for a total of ~ 14 hours of 24-hour sleep. Read 3 Things You Need to Know About Your 7 Month Old Baby’s Sleep