I Have Been Suffering While Urinating And It Burns A

I have been suffering while urinating and it burns a lot and recently I saw blood while urinating.Its the second time I'm seeing it but this time it was really thick and dark.Is it something to be worried about?Few months ago I went for check up and the Doctors said I had UTI and gave me antibiotics which I took and since then every month Once a while I'm having this burning sensation.I had never felt this way before.Or is it cause of my sexually life?I took birth control pill while I was having my period last month and that is when it all started.Please do reply me I'm really starting to get stress about all this things.Let me know what should I do.