I started feeling tired all the time plus I noticed im starting to gain weight, even though I exercise, what could cause this?

Tired + wt gain. These are symptoms that frequently reflect a starting clinical depression. Get a mental health evaluation before it gets worse.
Dear Gaining Weight. Our bodies are "programed" to hold onto weight for many reasons. My suggestion is that you get a thorough physical exam including a history of your health and your family's. Labwork and an EKG is essential. I do not know your age, but our ability to burn calories decreases with age, sometimes, we need to incrrease our exercise to get the same effect we did years ago. Stress may also contribute.
Gain weight -tired. A great many conditions can be the culprit. It is important to find out the cause so you can be treated in order to get well. For example you could be having a thyroid problem that could cause this. See your doctor to find out what is going wrong.