Hi there. First of all, what were the stictches for? A cut? Actual surgery? Is it over a joint? Alot of people think they have an infection after stitches but end up being a "stitch abscess" or stitch irritation. Understand that a stitch is a "foreign object" and your body does not like it...so going by redness and warm is not reliable because this is normal. It takes experience to pick up a small infection. If it is a big infection, it is the obvious....excessive foul smelling pus with fevers and chills. Look at the area you suspect.....it is superficial or deep? If superficial...low chance of infection. Does it "tunnel" down deeper? Some drainiage is normal...don't be alarmed. Mild soap and water and let air dry. If doesn't heal, see the surgeon that did the surgery.
Swelling is often a sign of infection, especially when it is accompanied by reddening of the skin. Marked tenderness and a burning sensation are also signs of infection and so are fever, coughing, headache and nausea.