Help please

Ok so I had my cycle Dec 4-10 I had unprotected sex on the 20th and he finished in me. On the 25 I got another 5 day period but it was a little lighter than normal. I took a pregnancy test and both the. Expensive and inexpensive were negative. I think I am freaking out but I would really appreciate some help. I’m also on the iud it’ll be time to replace it in march. Is there anyway I could be pregnant