Embarrassing & Confusing

Alright so, this isn't something I really want to share but I feel like I need to share because I have a serious question I need answered.

In August I thought I started what I thought was my period. I haven't had cramping since I was young and I was having very intense horrible pains. I thought it was just bad cramping and let it go and tried to just baby myself lol well about 5 days into it the pain had gotten increasingly worse. Night time was the worst and I couldn't sleep and was bawling my eyes out because of the pain. WORST PAIN OF MY LIFE. It got to the point where I knew something was wrong now and I probably should go in. Waited another day to see if it would go and ended up not even being able to walk properly. I thought it could be appendicitis because of the location. Ok so went to the ER because of the severe pain and they diagnosed me with PID caused by Chlamydia...the man I've been talking to for 6 months now got checked and his results came back negative..I have never cheated on him with anyone! So this is confusing the shit out of me. I contacted the last couple people before him to see if they had gotten checked and if I had possibly gotten it from them but they said that they have gotten checked and were clean.

So how did this happen? Did I have it for years and not no it? Has this happened to someone else? I'm posting anonymously because this isn't exactly something I want shared from my name. Thank you for reading this and please help.