In my experience with sweet n sour it's not the sauce itself that gives that obvious pineapple flavor, it's the pineapple chunks... Try this:
2/3 cup sugar
1/4 cup ketchup
1/3 pineapple juice
1/2 cup cider vinegar
2 TBS soy sauce
1 clove crushed garlic
1 TBS veg oil
Mix first 5 ingredients together... Heat oil in a pan, brown garlic, discard... Add your mixture to pan and bring to a boil...
Mix 2 TBS cornstarch, and 1/3 cup of water, and add to sauce, stirring constantly until thickened...
Hope this helps, let me know...