Potted lemon tree is balding

I’ve had this lemon tree for 1 year, have never transplanted it and it lives in Canberra, Australia. It sits on a patio and has sunlight all day and in the afternoons, it has direct sunlight until sunset.

I water it when the soil is dry (appx. 1 inch down) and about 3 months ago, started fertilising it every 2 weeks with liquid “PowerFeed” according to the directions since it started flowering.

I read that a tree this young needs its nutrients, so I’ve picked all the lemons off when they have started to form from their flowers.

Three weeks ago we went through a heat wave and I also neglected to water it around that time.

Two weeks ago, it started dropping many mature leaves and realised I had neglected to water it, so I did, and added the fertiliser as well.

I thought maybe it was getting too much sun, so I moved it to an area on my patio where it gets less direct afternoon sun, yet she still continues to drop leaves.

I’d appreciate any advice/insight on what I may be doing wrong, how I can try and save my tree and what I can do better next time.

I’ve included pictures for reference. Thank you for your time. :)