it sounds to me that the problem is very likely you let it dry out too much, now your soil is likely hydrophobic or has pockets that are and this is stopping your plant from getting enough water. My bet is you water to runoff but seem to get a lot more runoff than you expect. besides up-potting you may want to thoroughly water the pots.
to help with the hydrophobic soil add some aloe, yucca, drop of dish soap to your water and when you water instead of just pouring the entire amount of water in the pot, divide it into a few pours of water, pour some on, really let it be absorbed then add more and wait until runoff