a streak of blood in your stool after straining is not something you need to worry about. it is probably due to hemorrhoids which are very common during pregnancy and usually not a big deal. if they become a big problem then you can use an over the counter cream like preparation h which generally helps. but most women only have problems that are minor. if however you suspect that it was vaginal blood, you should call your actor, but based on what you said it doesn't sound like that was the issue for you. I hope this was helpful, please let me know if you have any more questions.