1st issue: It would seem that your 0.045 btc is made up of a LOT of inputs... how many individual inputs do you see if you click on the "Coins" tab ("View -> Show Coins", if you can't see the "Coins" tab)... I'm going to guess you have upwards of 10-15 inputs...
Each input you have, will be adding something like 148 bytes to any transaction you're attempting to create. 10 inputs will mean a transaction size of around 1500 bytes... as fees are determined on a sats/byte or btc/kB basis, it follows that the larger the transaction data size in bytes... the larger your fee is going to be.
2nd issue. Due to the current network congestion, 150,000+ unconfirmed transactions etc... network fees have risen to simply INSANE levels... fees have been upwards of 1500 sats/byte... even now the recommended fees are like 1000 sats/byte...
now... lets do the math... say you only have 10 inputs -> 1500 byte transaction... fee of 1000 sats/byte... -> fee = 1500 * 1000 = 1,500,000 sats = 0.015 BTC!!?!
If you set up your transaction, and click the "preview" button, it should show the size of the transaction in bytes... if it is as I suspect (ie. > 1500-2000 bytes), it would appear your 0.045 BTC is made up of a lot of dust sized inputs
Your solutions are either use a "manual" fee and put in a tiny fee and wait about 4 or 5 days for your transaction to confirm because it will get stuck with such a "tiny" fee... or wait until the network is not as congested and fees return to a more reasonable level
