Vaginal discharge

Here's the deal. I've recently, within the past week, had sex for the first time since LO was born(5 months) and stopped taking my anti-depressants. I'm also breastfeeding and on Implanon. About three days ago, I started getting a lot of runny, slightly yellow discharge. It's too early for it to be a pregnancy symptom, right? It was less than a week ago, I'm on Implanon, breastfeeding with no period, it lasted just a few minutes and he didn't orgasm, so I'm fairly certain I'm not pregnant. My doctor told me that I could have different discharge while I'm nursing, but did anyone else have it start suddenly after several months? Dr. Google says it may be my body trying to get a period. There's no strange smell. If it were you, at what point would you say it isn't normal and go to a doctor?