when to go to the hospital

so im 35 weeks today, i been having back pain on and off today. i just left the hospital yesterday and they did say i was having contractions but i wasn’t feeling them then. but today my back just been hurting, coming and going.. idk how to “time contractions” or anything. this is my first baby and im kinda scared.. idk what to do. i just been trying to go to sleep.. i can still feel my baby move but also having cramps and back pain.. any suggestions?? i can’t just call my ob bc i haven’t seen my new one yet due to the weather. and i also feel really nauseous