So I'm in a fight with bug bears and they're constantly trying to trip my guys. Whenever they do this though they're allowed to instantly attack the same turn they triped them and gives me 0 attack of oppotunities. Then if i try to trip them they all get attack of oppotunities and if im succsessful I get no extra attack on the bugbear that was tripped. Whats with this mechanic being so obviously onesided?

The rules are, you need to have the Improved Trip feat to not provoke AoO and make an attack after a successful trip attack. Alternatively, you can use weapons that do not provoke AoO (from the top of my head, spiked chain in temple+ qualifies), however, you won't be getting free attack (unless you had taken the aforementioned improved trip feat).