All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Family planning is permissible only to gain benefits and avoid harms as stipulated in the Sharee'ah. For instance, when a woman becomes too ill or gets exhausted due to consecutive pregnancies, or am early pregnancy that could harm the fetus itself etc.
But if the purpose of family planning is to decrease the human race it is then prohibited. Because this practice contradicts the Will of Allah and the rulings of the Sharee'ah which urge Muslims to increase the progeny.
This viewpoint is confirmed by the Islamic Fiqh Council and by the Permanent Committee of Islamic Research and Iftaa.
You may refer to a reliable experienced doctor to know the best way for family planning.
Allah knows best.