I've started to get nausea with PMS, just in the last couple years. Your body does change, so I actually don't consider it a pregnancy symptom until I'm pretty good and late. :-) And the sore boobs and tiredness I get anyway.
For me though, given a few days, you can feel the difference between normal PMS and something else going on. The breast pain is just not the same, the fatigue much more intense, etc.
I'd suggest taking a pregnancy test! Six weeks is plenty late enough to be feeling very, very prego.
I would also recommend taking a test. They could also be normal pms symptoms even if you never had it before since your body changes.
Yes those are all signs of being pregnant I am 6 weeks and I have all those and a few more so I think you should take a test then if it says no then go to a doctor.