Help!! When to worry about Braxton Hicks?

I'm 28wks with baby #2. For the past few days I have had Braxton Hicks on and off. They're slightly more uncomfortable then usual but nothing painful. I started to worry a little when they began to feel like they had a pattern and I started to feel the Braxton Hicks in my lower back. At least 3-4 a hour. Also am i to early to "drop"? I feel like I have already? Just wanting opinions and to know if I'm worrying for nothing or if I should ring midwife?