There is no nothing wrong with getting pregnant whilst breastfeeding
Question

                I have a son who is 19 months old, and I would like to know: is it permissible for me to get pregnant whilst I am breastfeeding my son? What is the ruling if I get pregnant and cannot continue breastfeeding him? Do I have to wait until I complete two years of breastfeeding, and then try to get pregnant?.
Praise be to Allah.
      It is permissible for a man to have intercourse with his 
      wife who is breastfeeding, and there is nothing wrong with it. And there 
      is nothing wrong with a woman breastfeeding when pregnant, because of the 
      report narrated by Muslim (1442) from Judaamah bint Wahb al-Asadiyyah (may 
      Allah be pleased with her), that she heard the Messenger of Allah 
      (blessings and peace of Allah be upon him) say: “I was thinking of 
      forbidding intercourse with a breastfeeding woman, until it occurred to me 
      that the Romans and Persians do that and it does not harm their 
      children.” 

    But the woman should examine her own case and her ability to 
    put up with that, and she has to weigh up her duty towards her nursing 
    infant and what she herself will need during the period of pregnancy. If she 
    thinks that she may not be able to balance matters, or she thinks that it 
    will harm her, then there is no reason why she should not put off getting 
    pregnant for a while, so that she can finish breastfeeding, then start a new 
    pregnancy. 

    Ibn Jibreen (may Allah have mercy on him) was asked: 

    I am a woman with six children, and in most cases I got 
    pregnant before completing the breastfeeding of the previous child -- before 
    the end of the two years -- and I want to use the so-called “coil” 
    [intra-uterine device, a form of contraception that is inserted in the 
    uterus] to prevent pregnancy for two years only. What is the Islamic ruling 
    on that? 

    Answer: 

    There is no reason why you should not do that, if both 
    spouses agree to it, and they are certain that it will not cause any harm to 
    the uterus or prevent having any children in the future and so on. End 
    quote. 

    Fataawa al-Shaykh Ibn Jibreen, 
    96/2 

    See also the answer to question no.
    21203. 

    And Allah knows best.