For one thing, Farmgirl, it looks like it's getting too little light. I would try to put it where it gets several hours of direct sunlight in the morning. Indoors, once every two week watering is probably too much, also. I would probably go 1-2 months between soakings, depending on temps and humidity. If the base of the stemsare black and mushy, you may have to unpot the plant, cut out all the mushy parts, and dust them with wettable sulfur dust. Let them dry for a week, then repot in a fast-draining mix--commercial cactus mix, if available. If that's not available, then mix together 1 part coarse sand, 1 part perlite, pumice, or volcanic cinders, and two parts regular potting soil. The mix should be moist but not soggy when you pot it, but don't water for a month after potting. You'll know that it has new roots when new growth starts.

Thank you so much! I'll have a go at these suggestions. Light is definitely an issue, so you're right on there. Will see what I can do. Thanks again!