1-2 years. Typically, water quality is a big reason why. If you have cleaner water or filter on your home, then it would need it every 2 years.
Low water pressure to blame when in actuality you have low water volume. Volume issues usually occur when a valve is not fully open or there is some obstruction in the line, The obstruction could be in the pipes, valves, cartridges or aerators.
In the cabinet under the sink you should see 2 oblong (usually chrome) handles, turn both valves clockwise until they stop. Some valves are only a 1/4 turn to shut off and some you have to turn multiple times until they close.
Drains collect all the worst stuff from your day and put it in your pipes, a lot of that stuff sticks to the pipes and mixes with soap scum which then decays and starts to smell. You can pour bleach down your drain to immediately kill the bacteria and smells that have built up on the surface, but the best way to prevent the smells from accumulating is to use an enzyme in your drains regularly. The enzymes are a living organism that eat all organic material, with regular dosing of enzymes drains should remain free of all smells and most blockages.