Pre cum

So I just got my Nexplanon implant out about three days ago, me and my man have never used protection before and when we have sex he always says he’s not sure if he came or not. I have irregular periods due to when I had the nexplanon in so usually apps give me incorrect days for when I’m ovulating. I also started bleeding when me and him had sex a day after I got my birth control out, I was bleeding heavy but it lasted for ten minutes before I just stopped bleeding and it’s been a day and I haven’t bled since. I am getting all the physical and mental parts of having a period like the PMS, bloating,cramps,headaches,and back aches but like I said I have irregular periods so I’m not sure if I have one coming or if I’m just getting symptoms of it. I took three ovulation test the last few days… the first day was 0.32, the next day was 0.98,and this morning it was 0.62 but I have a feeling that the 0.98 was incorrect but anyways…my question is, what are the chances of me getting pregnant from pre cum? I’ve read it’s about 20% but I just wanted to know if someone else knew somthing🤷‍♀️.