3 months after double jaw surgery cleaning my teeth toothbrush hit behind my lower teeth inside my mouth on the ramus (?) quite a few times hard, could that push lower jaw back?

No: Hitting you r jaw with your toothbrush will not do that. Short of major trauma there is nothing you can do that will "push your lower jaw back".

Not likely: The jaw can be moved upwards, downwards, forwards and rarely backwards because of the anatomical structure, especially after the orthognatic surgery.

No: sufficient healing has occurred so you could not do any damage.

No: No. the bones that were sectioned in that operation have solidly healed.

Not likely: Very unlikely that there is any concern after 3 months. Also, you may be stabilized with wires or plates or screws and it would not be possible to move the jaw. Of course, be careful, but you won't move your jaw with the toothbrush. Good Luck.

Don't worry: The bone had knit together after the first 6 weeks, and now it is reorganizing and maturing. Please try not to traumatize tissues by overly-aggressive brushing, but do clean thoroughly and carefully. Avoid contact sports. Your Oral Surgeon knows you best. Call his/her office to see if they would like to see you for a reevaluation.

Short answer: No: when jaw surgery is done...metal screws and plates are used to fix the repositioned parts. you wouldnt be able to generate enough force from brushing your teeth in that manner to seperate those parts and cause your lower jaw to go back

Not likely: once you have healed from orthognathic surgery your jaw will not go back with minor trauma.