Outlets and switchs are usually anchored to studs. Find the one closest to the stud you are looking for, without a door in between. Take the cover plate off - be careful unless you turn the power off. The stud will be on one side. The boxes are thin. You may see the stud by the plaster/drywall.
Your stud should be some multiple of 16 inches(maybe 24) from here.
A 2x4 stud is really 1 1/2 inches by 3 1/2 inches. If you are poking every 2 inches you could easily skip right over a stud.
Doorways and windows have two studs on either side of the opening. The first stud from here may be less than 16 inches.