Would I know for sure if I stepped on a needle?

I've been really struggling lately with my OCD and HA lately. The past week and a half have been hell and today is my second day on 50mg of Zoloft (gonna go up to 100mg in a week). I went out to eat with my folks yesterday evening and was in a rougher part of town. On our way out of the restaurant into the parking lot my left heel "shifted" in a way (I don't know how to describe it, maybe a mistep moving the muscle a little bit) and I instantly freaked out thinking I had stepped on a needle.

I checked behind me to see if I saw anything, and I didn't. (My mom is aware of my OCD and checked also and said "there's nothing there.") and I checked the bottom of my shoes and didn't find any evidence of a needle there. I checked also when I got home the soles of my feet which looked just fine and rubbed some alcohol over them to be sure and nothing stung.

But this morning at about four am I couldn't sleep and found that there was pain on pressure in my Left heel in a concentrated point! I again went to look at my foot and there is no evidence of a bruise or anything but I still am freaking out over it. :(

I'm deathly afraid of blood-bourne diseases and the idea of possibly contracting something and not knowing that I have it and giving it to my boyfriend is unbearable.

If something punctures the thick skin on the sole of your foot, you'll know. The pain is truly horrendous.

Just wanted to say, my first week on sertraline ( Zoloft) my ocd was 10x magnified, I actually thought I was going to be sectioned.
Read my thread sertraline diary if you want some hope. But trust me when I say do not believe anything your brain tells you for at least two weeks. Mine told me I’d had sex with other people and forgot, that i was a child molesterer and everything.
4 weeks on and I now look at those thoughts and think wow what a crazy ride.
I would say practice mindfulness constantly for the next two weeks but I remember being in your shoes 4 weeks ago and that wouldn’t have even touched the sides. But what did help was some Valium/diazepam 3 times a day for the first week and then slowly reducing.
You will get through this. I won’t offer reassurance on the needle as we both know it will only feed it.
But what I will say is keep your chin up it gets better I promise. I’m proof

As difficult as it is, resist the urge to seek reassurance. This obsession will pass.