If your bench technique is good, you need more muscle to move more weight. What strikes me is the low amount of protein you eat. I think you should eat more protein, at 90kg I would aim for 200-250g as a start and then adjust from there. Of course you can also slowly go up with your protein intake, depending on which way suits you best. Maybe you can get away with less, but that privilege is usually reserved to the younger people with good sleep and little life stress.
Also I think the additional exercises for the chest muscles are important, so do not skip on the flies and other accessory exercises, but maybe I am interpreting too much into "just me and the power rack".
These things aside, there can be of course other issues with the bench. If technique degrades with higher intensities, it could also be possible that you either need more practice (so keep doing what you are doing and try to maximize muscle mass in the process) or that you practice bad technique, which is not sustainable at higher weights. For this I recommend that you at film yourself, but maybe you already have a hunch from last competition.