27 weeks and still no Braxton hicks?

It's probably a wierd thing to worry about but I haven't felt Braxton hicks contractions yet. During my 20 week ultrasound my doctor said I was getting one but I couldn't feel anything. I'm afraid when I start getting them I'll think I'm in real labor since I'm in third trimester now. Or that when I get real contractions I'll think I'm just getting Braxton hicks since I don't know what they feel like. Any tips? Will I know the difference even though I've never felt them?