What Causes Bruises All Over The Body Along With Nosebleeds?

My 3 year old son has been very clumsy and gets random bruising along with all that he seems very sickly we can get cold and get over quickly but he seems to go from bad to worse and like clock work always moves into his chest so we have to treat it with a nebulizer. we have also noticed an increase in nose bleeds and he seems to be loopy like he goes somewhere else. I know some if not all could be normal I am a mother of 4 but, he is the only one who seems to be sickly and so clumsy. he is a twin and was born 5 weeks early and spent 4 almost 5 weeks in the NICU but I don't think that would still be apart of it. I just want to see what it could be.