Im 26 weeks and had a 1 time spotting

Hi.. im 26 weeks now. I had spotting about 3 days ago(red then brownish red) Rush to the doc and he gave injection to quicken the liver development for my baby.. and also injections to support pregnancy He gave me meds to stop contraction, antibiotics and also im on ultrogestran. So far no more spotting. But i do wonder why is there spotting and should i worry.. #firstbaby