Yellow vaginal discharge. Should i do?

Previous condition :- I had white discharge ever since I got my periods. I went to a doctor after one year of my periods she said gave me some medicine and said that it is normal for some people. You will have discharge for whole life. I could feel it was not normal. I always had this feeling that I am having periods all the time with white coloured blood. And I had immense back pain always. I could not do any work that included strength ,without having pain in my lower back portion . My periods were also for 7-8 days . Then I went to another doctor and she gave me a good treatment which eased my back pain and my blood flow went to normal and for 4-5 days max. White discharge was still there but it was not as much as it was earlier. She said that two to three days of discharge a month is normal. But now I am having yellow discharge on a regular basis and it has foul smell and I also get tired too soon And I am afraid if my body is suffering from something serious. What should I do?