I've lost some weight recently by cutting back on crap food etc.
I've been doing pushups for a good while now, but I haven't improved in ages,

I started off being able to to do three or four strict pushups, now at a stretch I could do 20, but that would be a struggle,

I've tried increasing by one a day, no good, doing sets at different times of the day, no good,
I then tried this https://hundredpushups.com/week1.html

I can't get past day one of week two on this,
It says that I'm ready for week 3 if I can do 16 push ups but I can't through the sets on here,

It's frustrating as I actually think I'm getting worse instead of better,

And just to be clear, im not doing this thinking I'm gonna get all pumped, I just like the idea of functional strength, and of being fit to do them,

Thanks in advance for any replies