When you created the wallet did you write down the seed phrase on a piece of paper, and store it somewhere to which only you have access?  If you are correct that you don't have a malicious version of Electrum, then I would suspect that someone may have found your seed phrase.  Is that possible?

The other thing you said is that you downloaded it from the official site, do you mean you downloaded the APK file, or did you click the link to google play?