When I was little I was healthy but when I reached my teens I developed allergies, scoliosis, weak joints, and breathing problems. What could cause it?

Allergies, scoliosis. While some children develop asthma in infancy, it is more typical for allergies like hayfever to develop in adolescence and young adulthood. Presumably, this is due to hormonal changes which then cause changes in the immune system. Scoliosis is not related to allergies but can worsen in teens as a result of growth spurts occurring at this time which can affect bone and joint development.