go see Bhadra then see yogi and reggie to get the mission the mouth of madness (look for B or a Y on your map)
after that you'll get another Amita mission called the sleeping saints
if you see a Longunius mission (look for an L )pop up DO it too as some missions will require others to be completed . also if you see no letter on your map always keep an eye out for a yellow symbol if two crossed swords , those are balance of power missions where you must choose who leads the golden path either choose Amita's mission or Sabals . the missions between the two are different and change the outcome of the game
also after the Chemistry mission look for an orange W those are the Willis missions and you must do all 3 before you can get to A key to the North