It's too soon. Also, for a baby "sleeping thru the night" is generally like 5 hour stretches. I have a 6 month old who doesn't do that. At 7 weeks it wasn't even an idea.
Are you breastfeeding or formula? breastmilk digests faster so that may be why. my son is formula fed and he's been sleeping from about 10pm to 6am for about a month and a half and he's 3 months. and don't try baby cereal bc it's useless and they don't need it.
7 week old's stomachs aren't big enough to stay full for very long. babies can't start anything heavier than formula or breastmilk for at least 4 months.