If it was from pregnancy, you wouldn't be lactating this soon, if that's your question.
Sometimes, discharge is normal. Sometimes it isn't. However, since it's new to you, you should get it checked out. Here are some things that could cause this - https://www.webmd.com/women/guide/breast-nipple-discharge#1
When you see your doctor, you should talk about birth control options because relying on your partner to pull out isn't a great method of pregnancy prevention. Even when done perfectly, there is still a really good chance you could get pregnant, as pre-ejaculate fluid contains sperm. It also offers no protection against STIs.
Let us know what the doctor says about the discharge.
Plan B is a big whopping dose of hormones which is how it works and is effective. But then your body has to deal with all those extra hormones. This usually results in things like an irregular period which can be the case for 2 to 3 full months after taking it. And clear discharge from nipples could be the result of hormonal changes. Do not be surprised if your period is also late. You can take a test to see if you are pregnant that should give you an accurate result 2.5 weeks after the intercourse in question. The pull out method does not prevent pregnancy. The penis emits small amounts of sperm before the big ejaculation and it's enough to get you pregnant. So, keep that in mind moving forward.
If you continue to have this discharge, get yourself checked by your doctor. I had this unrelated to Plan B, pregnancy or sex myself. I had what was called galactorrhea . This can happen when a woman has a small, non cancerous, non dangerous no big deal little tumor in their pituitary gland. I had an MRI looking for that. I didn't have it. So, when looking at my blood work, it was determined that I had a natural production of too much estrogen and a slow acting thyroid. https://www.mayoclinic.org/diseases-conditions/galactorrhea/symptoms-causes/syc-20350431
See if this gets better once the Plan B has worked it's way out of your system. If you still have lactation and took that pregnancy test and it's negative, then talk to your doctor. But I really am guessing it is the pill. And stress also adds to it.