What are the signs that you should not continue to have sex in the 1st trimester? what do i look for? should it be avoided all together?

Enjoy yourself: sexual intercourse is fine during the first trimester and actually, throughout your entire pregnancy. Obviously bleeding and pain are red flags. Position changes are important during the last trimester and prior to term, aggressive intercourse "might" induce labor. Many women become more sexual during the first 2 trimesters and likewise, this is normal.