18 month old with green stringy slimey poop?

My 18 month old son has had strange bowel movements for the past week. They are green and have like stringy slime or mucus. He is acting fine and doesn't seem to be sick or anything. He hasn't been eating anything different than usual. What could be causing this and should I be worried about it? I plan to call his doctor on Monday but I just wanted some thoughts in the mean time. Oh and he did have some type of viral thing like 2 weeks ago. His doctor said it was a viral fever, he had a temperature of 103 for 3 days. He has been fine since then. Could that illness from 2 weeks ago have anything to do with this mucus in his poop?