Clementine mandarins are not "sterile", you can certainly start seeds from a Clementine. However, Clementine madarins are monoembryonic, so you're going to get a hybrid of a Clementine and whatever other citrus happened to be nearby, and pollinated the flower that produced that fruit with the seeds you're planting.

If you would post photos, we can help you a bit better. Have you checked to see if perhaps you're dealing with root rot? Check the roots of your tree to see if they're water logged. If so, I would try to transplant in better-draining potting medium. If you search the forum for "511" mix, you will find the recipe for this mix, which works very well for indoor container citrus. Is it warm enough for you where you live (you do not have your location enter in your "Zone" field) to be able to put your citrus tree outside to get some sunshine? Are you fertilizing, and if so, with what and how frequently? We need more info in order to help you out.

Patty S.

I honestly don't know what root-rot would look like... I did notice that the pot it was in was not draining well, because the soil was always moist, so I transplanted it into my greenhouse garden, which drains exceptionally well; it now shares 15 cubic feet of soil (1 part organic compost, 1 part peat, 1 part vermiculite, mildly acidic) with a few radishes and lettuce. I used an 8-11-11 fertilizer monthly when it was in the pot, but I have not fertilized it since the transplant (about 3 weeks). The greenhouse is south-facing, but still only gets about 8 hours of sunlight in the off-seasons, so I augment it with "high-output" T5 grow lamps for two hours in the morning and evening.

This is a close up of the main stem.

bump

You may have been over-fertilizing it. But that wouldn't cause the problem it is having. Part of the problem may be shock from being transplanted and moved.