L., I am a licensed nail tech and I believe you have the following. I am NOT a doctor and would need to see your nails personally to recommend the better solution for your needs. This is what I found to assist you...AGAIN, I AM NOT A DOCTOR.
Onychoschizia or splitting of the fingernails is a common problem seen by dermatologists. The term onychoschizia includes splitting, brittle, soft or thin nails. Onychoschizia is more common in women.
Only very rarely are internal disease or vitamin deficiencies the reason (iron deficiency is the most common). One tip is that if the fingernails split, but the toenails are strong, then an external factor is the cause. Basically brittle nails can be divided into dry and brittle (too little moisture) and soft and brittle (often too much moisture).
The usual cause is repeated wetting and drying of the fingernails. This makes them dry and brittle. This is often worse in low humidity and in the winter (dry heat). The best treatment is to apply lotions containing alpha-hydroxy acids or lanolin containing lotions such as "Elon" (by the "Dartmouth" company) to the nails after soaking nails in water for 5 minutes and after getting the hands wet.
Try to wear gloves when performing household chores that involve getting the hands wet to avoid repeated wetting and drying of the nails. Cotton lined rubber gloves can be purchased in stores.
If soft, consider that the nails may be getting too much moisture or being damaged by chemicals such as detergents, cleaning fluids and nail polish removers (the acetone containing removers are somewhat worse than acetone free). Some feel that once a week application of clear nail prep once a week may help. Nail polishes with nylon fibers in them may add strength.
Be gentle to you nails. Shape and file the nails with a very fine file and round the tips in a gentle curve. Daily filing of snags or irregularities helps to prevent further breakage or splitting. Avoid metal instruments on the nail surface to push back the cuticle. If the nails are "buffed" do this in the same direction as the nail grows and not in a "back and forth" motion because this can cause nail splitting.
Biotin (a vitamin) taken by mouth is beneficial. Gets the "Biotin ultra" 1 mg. size as it also comes as much smaller pills and take 2 or three a day. It takes at least 6 months, but does really help at least 1/3 of the time. Do not take this if you are pregnant. Calcium, colloidal minerals, and/or gelatin don't help consistently.