Implantation or spotting

I want to start with I am on nexplanon and when I have sex with my boyfriend we always use a condom and he always pulls out with the condom on. We had sex a few days ago and when we did I started off by giving him a blow job but he didn’t come. Well anyways we were making out after that and while we were having sex I got dry so he used his spit. Right away as soon as he touched me with it I freaked out and went and wiped off. We got a new condom and finished like a minute later. I’m afraid that I could have got precum in my mouth and when we kissed it transferred to him and then when he spit it was transferred to my vaginal area. The next day I noticed a little pink when I wiped and then the day after that I had blood in my underwear so I used a tampon. It didn’t fill up but there would have been enough there to ruin my underwear. The next two days it was back to that pink discharge looking stuff when I wipe. So I decided to feel around up there and it’s a lot darker discharge that isn’t coming out of my body. Since it’s been going on for four days, is that just spotting from my birth control and isn’t that too soon after sex anyways to see implantation bleeding. My sister just found out she’s pregnant and I’m freaking out because I don’t want to be pregnant yet until I’m married