Having definitely gotten out for $0 on the free tier, it sounds like you somehow ended up with other services or on an instance type that was not free tier eligible.
Only this many cents to use this thing, which, heh, I guess it requires this thing too, and this thing, and this thing ... man, some of these cents are adding up. Oh, a "NAT Gateway" is $30/mo? Well, OK. Keep going for a few weeks and you're staring down a bill for a rather scary number of cents while the CFO's angry rants can be heard half-way across the office.
There are entire consultancies that specialize in decoding AWS bills. Let's not pull leg here.