Here is how a cycle works for the typical woman. Day ONE of your period is Cycle Day One. You count from there. With a cycle of typical length, most women ovulate around day 14. You ovulate for 24 to 48 hours and once ovulation is over, you can not become pregnant in theory although can never rely on that as you can ovulate later than your norm or have a rare second egg. (meaning, there is no safe time in a woman's cycle to have unprotected sex). As you probably know, sperm lives for around 5 days so you can get pregnant if you've had unprotected sex a week before you ovulate. Implantation bleeding is said to happen but is actually pretty rare. I've not got a single friend that ever had it nor did I. And it is just a tinge of blood if it does. Brown mid cycle is OLD blood and more indicative of spotting and hormonal problems. Which wounds like you may have since you have few periods and hadn't had one for the span of 2 years. Do you see a doctor for these things? You should. Unprotected sex even if you have hormonal challenges like you describe isn't wise unless you want a baby. You just don't know WHEN you will ovulate. And you are right, pull out method isn't a method because it doesn't work to prevent pregnancy. When you ARE trying to have a baby, you also should not have sex daily as that takes a toll on sperm count. They say to have sex every other day when trying for pregnancy for sperm count. Anyway, hopefully somewhere in this I've answered your question. good luck