If you have any more than 4 an hour you should speak to your midwife/doc in case it is early labour
Having 20 a day is a bit much, braxton hicks like that are pretty normal though, but definitly mention it to your doctor tommorow.
Usually there a bit random but if they don't hurt I think ur ok I've had a couple on and off I'm 32 weeks and mine actually have hurt but there random and its usually like one or two at the most. The only thing I can recomend is drinking a lot of water and laying on ur left side usually that makes them go away.