I'm not too sure but I read some where that the set of 4 springs, 2 are for the back and the other 2 are for the front. Have you made sure you've used to correct springs on the correct half of the car?
are you checking this on a proper flat surface? did u upgrade your shocks?
maybe one if your shocks has packed in buddy, wear and tear probobaly, i would maybe look into it a bit further if i was you, when the shocks packed in on my old proton i found this out by bouncing the car from each corner of the car and the shocks that where packed in made a big clicking noise, try that?
the shocks wont affect the height of the car (unless they,re siezing).
are the springs still seated fully in the spiral shaped seats ? (top and bottom)
i swear mine are odd.. my passanger side looks lower than the drivers side :S altough could be tyre presurres?