My son has had excema in the past, particularly in the winter months. I use a really great over the counter cream - Aveeno for Excema for babies. It works well. Maybe give it a try. The symptoms you describe sound much like my 2 1/2 year old sons, and it too flares up and then goes away. Please stay away from Petroleum based products - I absolutely know your Dr. would tell you that. They are not good for any sort of rash as they do not allow the skin to breathe.
The doc told me its eczema thats why i tried a little cortizone but im not very happy using it and the dermatologist told me acne but it looks nothing like it, plus it flares up at different times for no apparent reason i am going through a process of elimination now with certain food as i dont really know what else to try. I avoid all harsh bath products and creams. He has had a little cold but fine now no fever and otherwise very well.
Has he been sick lately any other symptoms, teething in babies can be another cause, is it hot where you live as that would make his face red. The creams may be a bit strong, you could try some vaseline .Have they suggested food intolerance as that may be another factor .