Recently, my home-made bread has started going soft and squishy, with a yeasty smell, after 3 or 4 days. I have tried adjusting the type of flour, the type of yeast, the amount of yeast, the time of baking, the wetness of the dough, all to no avail. I am sefl-taught, have worked in a hotel as baker and have never had this problem before.

Any ideas on what the problem is?