Stephen Trimble gives us a shot of the internal weapons bay of the F-35.

This is intended to be the standard loadout, with one AMRAAM and one 2000 lb JDAM in each bay.

IIRC, with the 250 lb SDB, it can carry 4 per bay.

And yes, this appears to be a pretty small weapons load for an aircraft that has a maximum takeoff weight of 70,000 pounds, nearly that of the F-15 E, which can carry about 5 times the ordinance.