Hey ajaan, congratulations on your weight loss and the progress you've made thus far. Plateaus happen and they can be very frustrating. My first recommendation is to stop training push-ups 3 times a week. Now that you are no longer a beginner you need more rest between training sessions. Give yourself 3-4 days between each push-up workout so that you are training push-ups no more than 2x a week. At some point you may have to increase rest to where you are training push-ups once a week. That is what I have found that I need to do. I'm 51 by the way. Secondly, whenever you hit a plateau, slow down the reps. I often train as slow as 3 seconds down, pause for 2 seconds and then 3 seconds up. You don't have to go that slow, a cadence of 2-1-2 would be fine. You could even do 2 seconds down, pause 1 second, then go up as quickly as you always do. The point is, make the reps count. Training should not be about doing more reps and more weight, it's about building strength. MAKE THE REPS COUNT. Yes, I know, we know we are making progress when we see the reps and weights going up, but focus on the training and check your ego at the door.