What's normal when taking Brethine?

Jaxonsmomma2012

I've been taking brethine since I've been 28w. I'm used to it by now (not shaky and jumpy and such) but for the past week or so I've been getting contractions with the medicine and I brought it up to the doctor who didn't seem concerned at all.. Up until then I had zero contractions while taking the medicine.. And I was advised to take it every 6 hours.. It's not lasting 6 hours.. For three days now I've felt like my back is being split open almost and I've been having some intense contractions.. They're random contractions too and I haven't thought to even start timing them because I'm not getting them one right after the other.. I might get 2-3 in a row then go a bit and then have a few more.. There was a few last night that woke me up and took my breath away.. I can't get comfortable like I was able to before.. No matter how I lay in bed or shift or if I get up and move around I still hurt terribly. Is this normal with the brethine and being 34 weeks (tomorrow I'll be 34 weeks)?