One slow sink versus several
A single slow fixture is a local problem: the trap, the tailpiece, or the branch arm behind the wall. Hair and soap in a bathroom, grease and food in a kitchen.
Two or more fixtures draining slowly at once is a different situation. That points at the branch line they share, or at the main line, and it will get worse rather than better.
Why it gurgles
Gurgling means air is being pulled through the water in the trap because it cannot get in the normal way. Either the drain is partly blocked and creating suction, or the vent serving that fixture is obstructed.
A blocked vent is worth ruling out. It produces slow drainage and sewer odor without any blockage in the drain itself.
What not to do
Caustic drain openers sit on top of a full blockage rather than clearing it, generate heat inside the pipe, and make the line hazardous for whoever opens it next. On older pipe they can do real damage.
Repeatedly plunging a kitchen sink with a disposal on one side and no plug on the other just moves water between the bowls.
When it is worth calling
Same fixture blocking every few weeks means there is a physical reason - a sag, a bad slope, or a partial obstruction that a cable is only punching through rather than removing.
That is where camera inspection earns its cost: you find out whether you are buying another clearing in six weeks or a repair that ends it.