May be Braxton Hicks but keep timing. If the cramping/contractions start coming sooner than 5 min apart of for sure if your water breaks, go to the hospital. Are you aware of if you lost your 'plug' or not?
At 35 weeks it could be labor, but you should call your doctor and ask to be seen if you haven't already. Where are the cramps? Back, sides, low abdominal? When I went into labor with my first, it was like really bad menstrual cramps at first, but then it started around my back and before I knew it, it was all encompassing pain. I also had a kidney stone earlier in that pregnancy that felt similar so the only way to know for sure is for your doctor to check you out.