I Am Unhealthy

I don't smoke or drink I do however eat drink junk food at times and I am over weight. I keep having weird symptoms and just not as fit for my age as I should be .I have seen bigger than me and still able to do more and it really gets to me even see old people do and move about more than me I do try my best how do I build myself back up and feel more energetic as if I move to quickly puts strain on my legs and back and every where.