Before you try peas, try epsom salt first. Mix up one gallon of water and one teaspoon of epsom salt, letting the salt dissolve first. Put him into a small cup or container (the cup he came in from the pet store works great, so do disposable Gladware containers) and fill it with the epsom salt water. You can float him in his tank to keep him warm if you want. Change the water every single day, redoing the salt mixture each day, for five days. If he has not gone down in size, increase the epsom salt to two tsp per gallon and continue treatment for another five days. If he still hasn't gone down or passed waste, then post back and we'll talk other treatment like peas. If at any time during the treatment, he gets worse, post immediately.
Hope this helps.