Thanks for your query,
Braxton Hick's contraction are present althrough the pregnancy
. They are painless . But later on ,at the time of labour ,these contractions become painful, frequency increases and hence delivery. Intense pressure on back ,may occur during late pregnancy . Some times it may be a sign of onset of labour.Reddish discharge if starts, that also is a sign of onset of labour. So be in rest and be prepared.
Hope it helps..