Impossible to increase birthrates

Hi,
For the last six real months the population of my country is decreasing consistently. I can see that the death rate is always bigger than the birthrate, no matter how much I increase the health index, also salaries, goods quality, even social payment rates.
I tried to bring population from my slave country (spent three months doind that almost every game year) and also from conquered C3s. I just don't know what else I could do to revert it...
Thanks,

Country: Tocantins

Forgot to say that I am at WG world

Once your country is at a certain population, around 70 million it will naturally start to decline in population. This is caused by your population age distribution. If you have more older population and less population between 18-40 you will start to lose population. There are more elderly dying, and less population giving birth.

In the short term increasing healthcare will decrease the rate of decline but as time goes on your population age distribution will start to shift. There will be less Children and population between 18-40 and there will be more population over 40. This means that your country will suffer more losses in the future. Also your country will become economically less effective. More people will be retired and social security costs will go up. There will be less people in the work force. Yes, you won't need as many schools but the cost of healthcare and social security far outweigh the cost of education, and you will have