You won't get bed bugs from simply not washing your sheets as often as you should since bed bugs are not attracted to dirt and grime.
Bed Bugs can show up on clean beds and clean sheets as well so even if you keep your bed sheets and bed and bedroom and house clean you can still get bed bugs.
Bed Bugs are attracted to warmth, blood, and carbon dioxide.
Still you should wash your bed sheets once or twice per week to keep them clean and fresh because when you sleep in the bed sheets your bodily fluid such as sweat gets onto the bed sheets.
If you have bed bugs you can put dryer sheets under your bed sheets because the bed bugs hate the smell of dryer sheets and will stay away from them.
But still you should use some bed bug fogger or have an exterminator come into your house and get rid of the bed bugs using their equipment and expertise.