l get a lot of bloody noses usually when l have my allergies.
how do l get them to stop and what could be the cause?

You get them because your nose is too dry. If you have been taking medicines for your allergies, they clear up your sinuses, but sometimes too much. When your nose gets too dry, it uses blood to lubricate it. You could either try a saline nasal spray, or try a different allergy medicine that does not dry you up so much.