Braxton hicks?

So this is really weird and confusing. When I was pregnant with my son I went into preterm labor and the contractions felt like regular period cramps. When I went into labor and actually had him I had back pain and period like cramps but never, not even once, felt my belly get tight. The nurse put her hand on my stomach and said she felt my contractions, however I did not. I'm 13 weeks pregnant with baby #2 and for about 1 minute the other night my entire belly got tight and I felt a lot of pressure especially around my belly button. I've never felt a contraction in my belly before but what I felt seemed like a contraction. I looked up contraction at 13 weeks and found that Braxton hicks doesn't start until 3rd trimester so I'm really confused. I have not had any bleeding or cramping and it was an isolated incident that hasn't happened again. What do you think it was? Could it be super early Braxton hicks?