Intense, painful, but irregular contractions - is labor near?

I'm 35w3d pregnant. I've had Braxton Hicks contractions for the last several weeks, and they feel like mild menstrual cramps - uncomfortable, but not actually painful. The last couple of days, though, I've had a few contractions that *really* hurt. During these I haven't been able to speak, and I had to use breathing techniques I learned in my yoga class to get through the contractions. The intensity of these 'new' contractions made me wonder if labor was about to start. However, they're not occurring at a regular frequency, just a few a day.

Have any of you experienced this? Is it still Braxton Hicks contractions, or could labor be around the corner? My baby dropped a couple of weeks ago.

I'm a first-time mom, so I'm not entirely sure what to expect! Just wanted to ask here before I call my doctor. Thanks.