Very brittle nails???

So my finger nails are always very thin. Whenever I grow them out long, they split and tear, so I have to have them very short. I hate this because it looks awful and my fingers look stubby. I don’t know why they are so thin and brittle, I take multi vitamins, my nutrition and water intake is pretty good as well, I workout a lot and am in pretty good health overall. Is there something else I can do about this? Currently they are so short to the point my fingers would almost bleed. I use to just have my nails done and get a full set and just forget about my real nails, I have not done that I’m a few months but I really want to see if I can fix the problem.