2006 Suzuki Forenza on third thermostat

my thermostat has been replaced twice and now is overheating after about 6 weeks of the new one

I’ll assume the overheating preceded the new thermostat . . . ?

Assuming the new thermostat is working correctly, you may have a much more serious problem

Is your coolant level correct?

Good accessory drive belt tension?

No obvious coolant leaks?

Are your electric fans . . . I’m assuming you have 2 . . . both working?

If you are not in a position to check these things, then you’d be better off taking the car in to a reputable shop for a proper diagnosis and repair