How To Treat Pelvic Infection?

I was diagnosed with a pelvic infection last week. I was taking flagyl but i thought it was making my stomach hurt so I was switched to a gel that starts with and M. I have to insert it with an applicator. But come to find out the stomach pain was cramps and i started my period early. I had only use the gel once, then my period came. I waited until the 3rd day of my period to use it again because my flow was heavy. which is uncommon. All throughout my cycle I was lossing tissue. more than usual. And now that i am off my cycle I think im still losing tissue. No blood. Just a dark color massive amount of material covered in clear mucus. It comes out like a discharge. and its texture is dry and cannot easily break apart and is similar to fat on uncooked bacon...A week ago i had an std screening and it came back negative. whats wrong with me? im scared