What’s happening? Please help

So about 4 days ago I had a bit of red blood and thought it was my period ( period are very irregular and I’m not on my birth control, I came of the injection in feb) I put a tampon in and when I went to go and change hardly nothing was on it so I decided to put a pad on and carry on. The next day I had a brown patch in my knickers so once again I thought my period was coming but it was just playing up. The next day I wiped and nothing was there? Even today I still haven’t had any blood or brown discharge?

This hasn’t happened before I usually come on for about a week for when I do get my periods.

Please could someone tell me what it could be or if it’s happened to you?

(I last had sex around 27th April)