As long as the hCG hormone is in your body you'll have pregnancy symptoms. So tender breasts don't actually indicate too much--you'll have it regardless of pregnancy viability or not. As for your levels dropping and rising, it could be due to a vanishing twin or retained tissue. Get an ultrasound from your doctor and have him check your blood work again. If it shows them dropping and/or rising slowly, you'll likely need a D&C done.
Given that it is not rising very much, I would guess it is retained placental tissue. It's the placenta that produces the hCG reading, so it can go on for a while if a little bit of living tissue was still attached to the uterus.