Lets put an end to this confusion between being modest and having low self esteem. If you actually do think that you are "stupid, silly, fat and ugly", you most probably NOT and just having a low self esteem.

Now, good news! That's not the end of the world. Even if there no one that is saying you the opposite, attend to your reflection in the mirror and say out load all compliments of the world to lovely self. If it is hard... try with silent notes to yourself first: "You are the best!", "You CAN do it!", "You are so SMART!"... and hang them somewhere you check not less then twice a day. That's going to make your day! Think positive and don't forget to actually ACT! Good luck!