I need a script to run a specific action and save file as .jpg with SAME document name

Philip, thanks SO MUCH. Unfortunately, I was having problems with it because the action I was using saves a large version of the file (original size), then creates a new document, shrinks it, and performs more actions and saves a small version of the file. So what I did was create two separate actions, "savelarge" and "savesmall" and tried to get the script you just wrote to do both one after another. So we start with mydocument_PSD.psd and the script saves them as "mydocument_large.jpg" and "mydocument_small.jpg". It seems to be working but I wanted to make sure I wasn't messing anything up.

Do you see anything below that looks incorrect? Again, thanks sooo much.

#target photoshop; 

main(); 
function main(){ 
if(!documents.length) return; 
try{ 
    var path = activeDocument.path; 
    }catch(e){ 
        alert("This document has not been saved"); 
        return; 
        } 
if(activeDocument.name.toString().toLowerCase().search(/_psd\.psd$/) == -1){ 
    alert("Filename is not in the correct format"); 
    return; 
    } 
var fileName = activeDocument.name.toString().match(/[^_]*/); 
var savedState = activeDocument.activeHistoryState; 
//Amend with the correct action name and action set (case sensitive!) 


doAction("savelarge","Action Set"); 
////////////////////////////////////////////////////////////////////// 
SaveJPEG(File(path + "/" + fileName + "_large.jpg"),10); 
activeDocument.activeHistoryState = savedState; 

function SaveJPEG(saveFile, jpegQuality){ 
jpgSaveOptions = new JPEGSaveOptions(); 
jpgSaveOptions.embedColorProfile = true; 
jpgSaveOptions.formatOptions = FormatOptions.STANDARDBASELINE; 
jpgSaveOptions.matte = MatteType.NONE; 
jpgSaveOptions.quality = jpegQuality;  
activeDocument.saveAs(saveFile, jpgSaveOptions, true,Extension.LOWERCASE); 
}; 




var fileName2 = activeDocument.name.toString().match(/[^_]*/); 
var savedState2 = activeDocument.activeHistoryState; 
doAction("savesmall","Action Set"); 
////////////////////////////////////////////////////////////////////// 
SaveJPEG2(File(path + "/" + fileName2 + "_small.jpg"),10);
activeDocument.activeHistoryState = savedState2; 
};  
function SaveJPEG2(saveFile, jpegQuality){ 
jpgSaveOptions = new JPEGSaveOptions(); 
jpgSaveOptions.embedColorProfile = true; 
jpgSaveOptions.formatOptions = FormatOptions.STANDARDBASELINE; 
jpgSaveOptions.matte = MatteType.NONE; 
jpgSaveOptions.quality = jpegQuality;  
activeDocument.saveAs(saveFile, jpgSaveOptions, true,Extension.LOWERCASE); 
};