Pain at 33 weeks pregnant.

So the other day I went to hospital as I was experiencing contraction like pain and very bad back pain, they sent me home and said I had a bladder infection after monitoring me for an hour. so I have been taking antibiotics for that for 4 days. Now I'm experiencing lightening bolt pain in my left side only from my ovaries up to my belly button. I don't know if I should call again but I feel like I may be wasting their time. I'm 33 weeks and just not sure what to do. Any advice or suggestions?