I have 12mBTC but when I try to send a transaction, after I enter the amount (allocating enough for fees) Electrum says that I have only 2.63 mBTC. When I go back to check, every transaction I received is confirmed for more than a week, how do I fix this?
It might be, that you collected a lot of small transactions in your wallet. And if Electrum assembles a new transaction, it adds a fee, which is calculated in satoshis per byte, and for sure deducted from the amount you have. This way you can only spend less satoshis, than you actually have. In times of high fees, it does not make sense to create a tax. But today, as of July 2017, fees are very low, and you can give it another try. I posted a similar reply here: