We apply effective Lagrangians to calculate the J/\psi J/\psi-J/\psi\psi(2S)-J/\psi\psi(3770) coupled channels scattering amplitudes up to one loop. With them we perform partial wave decomposition, where constraints from unitarity, analyticity, and HQSS are considered. The pole parameters of the X(6900) are extracted. Our study shows that X(6900) has quantum number 0⁺⁺, and it is likely to be compact tetraquarks. Some other newly discovered hadrons, such as X(2370), Pc states, are also discussed.