What could be causing my constipation and bloating at 19, and do I need tests or treatment?

I'm 19 years old. I've had constipation on and off for years. Sometimes I don't have a bowel movement for 3–4 days. I often feel bloated, full, and lose my appetite until I pass stool. My stools vary between hard, normal, and loose. I don't usually have severe abdominal pain, but I feel better after a bowel movement. I exercise regularly, drink water, and eat around 1500–1600 calories a day. What could be causing this, and do I need any tests or treatment?"