I also put on a load of weight with the Depo shot and I had continual spotting. Tried Mirena coil but unexpected bleeding was still a problem for me. Tried a diaphram but my partner could sometimes feel the rim of it if we were in more (ahem) unusual positions. The pill is def my best option.
What about linking your pill taking to something you do every morning? Such as when you make a coffee or brush your teeth. That's what worked for me.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.