Just recently my sternum (bone in between breast) has been "cracking" several times a day and just started to hurt when this happens is this normal?

May be normal. The sternum takes about 10-12 wks after surgery. Occasional clicking with coughing may occur during the intial few wks. However redness and drainage may suggest something more sinister requiring urgent medical evaluation.
No it is not. You need to notify your surgeon. Timing from your surgery is very important. The clicking and pain may be a sign of infection or just non union or healing of the bone. Either way it is not normal to be clicking. Your surgeon will examine you and determine if you need further tests and also give you options for treatment.