Your gains stopping may be a sign, here are some others
inability to sleep at night when sleeping was never a problem before
digestive problems
actual reversal of progress--feeling weaker or more exhausted in the gym
sexual impotency--in extreme cases
women sometimes stop having their period on a regular schedule
lack of hunger
dandruff and dry skin
now these are just some and you may experience all or none of these symptoms. Overtraining is easy to overcome, give yourself a break, eat foods a bit higher in fat content but still keep a nutritious diet-don't eat fast food or processed crap. Take a multivitamin, sometimes a vitamin deficiency can mimic the symptoms of overtraining and the problem may just be a nutritional one. Take at least two days off, be lazy and eat solid nutritious food. Lots of green vegetables have many anti-dioxidants and vitamins that your body may be craving. Nutrition is a huge component in training and many people have trouble dialing it in because everybody has different needs.