Is nipple stimulation during early labour safe?

I'm 40 weeks pregnant today. I woke up with pretty painful consistent contractions this morning that lasted 4 hours. Got to 4-1-1 and started to head to the hospital... and then they friggen stopped. They have been on and off all day. Very sporadic. Anywhere from 10 minutes between to an hour between. Pretty damn painful though. I am wondering if nipple stimulation would help them progress more. But I'm worried because I've tried it twice today so far... and both times I played with my nipple for maybe a minute and then got a really intense, painful contraction. And then I would continue to get contractions every 15 minutes for an hour or so and then they stopped. But that's only from playing with one nipple for less than a minute.

So like is it safe? Should I try for longer? I dont know what to do lol.