Light bleeding

I was wondering if anyone had any experience with this. I’m currently exactly 18 weeks and as of yesterday I’ve been having some spotting. By spotting I mean microscopic spotting where you’d have to really look at it closely to see the pink streaks. Today I also had a very small line of red. I called my drs office and they told me to keep an eye out for it and to come in if it gets worse. I have no cramps just occasional very faint spotting. What should I do?