It's actually not uncommon to lose weight in early pregnancy, especially if you had PCOS before, because hormonal changes can shift things quite a bit, but 2kg in 7 weeks without morning sickness is worth checking in with your doctor about just to make sure baby is getting what he or she needs. Since you're eating well and healthily, your PD can monitor your scans to see if baby's growing on track, which is really the main thing to watch rather than your own weight at this stage. Many mums with PCOS have healthy pregnancies, so try not to worry too much yet, but definitely bring this up at your next checkup so they can keep an eye on things.
I lost 10kg throughout my whole pregnancy but my baby did grow well and came out at 3kg. I always try to eat quality food, and drink more water for my baby. It’s okay to eat junk food once in a while but moderately.