First, let me say, im not on steroids, all natural currently

secondly... i work out on a 2 days on 1 day off cycle, working every muscle group in either day one, or day 2 so each group gets 2 days of rest in between

now... my other exercises are on point, and i am slowly but surely increasing in strength/weight

but im having trouble with the barbell bench press... idk if its a plateau but its annoying as hell, and could use some insight

Now, Bench press for me is day 2

i do 4 sets, 13 reps (or as close as i can get to it) at 60kg, then an exhaustion set of however many reps i can do untill the muscle is spent at 40kg

i can get to 13 on set 1 and 2, but sets 3 and 4 im lucky if i get to 8... its been like this for a couple of months

any ideas?

and again, its only the bench press that im having issues with, my other chest exercises are fine and i keep getting stronger there