What are these pills called?

i got a hold of some pills (stole them from a dealer) thinking they were Ritalin but turns out they weren't, they were a light yellow-ish beige and were a rounded rectangle shape, all i can remember about what was imprinted on them was just an "N" on one side. if you can give me any idea about what these were id really appreciate it, Ive been trying to figure it out for a while now. i took some when i thought it was Ritalin, and ended up overdosing (nothing too bad vomiting, headache, dizziness) i cant sleep and i have no appetite. ill answer any more questions you may have :3