I had a cactus at work since the end of March. It is my first cactus and I don't really know if I was watering it correctly or if I missed something else, but now it's turned yellow and became softer. I googled around, but I can't tell if I'm identifying the problem correctly and if this is a case of overwatering, some sites say that all that's left is to dispose of the cactus, other say to just leave it for some days.
The question is, is there anything I can do to help it? And how can I prevent this from happening.
Some info: the cactus is on the table, about 2-2.5 meters from a window which more often than not has its blinds shut. Also, the last couple of weeks have been quite hot, so the window was often opened. There may have been draft from time to time, but not for long periods of time. I've been watering it two times a month, every other Friday, until I saw a drop or two of water come out of the drainage hole in the bottom of the pot. I don't know how much water it was precisely, but if I had to guess, I'd say about 100 ml each time. Nothing else has been done since I bought it. At the moment the ground it completely dry and I was going to water it again this Friday.
edit: Also, I sprayed it with water two or three times during the time it was here.