Everyone is different regarding restarting cycles after having a baby and breastfeeding, so you never know until your cycles start and become regulated when your fertile window is.
As far as finding out if you were pregnant, think of it like if you were TRYING to conceive.
If you coincidentally ovulated the same day you had sex then 9 days later is probably the earliest you might get a positive hpt. For the latest a test might tell you, as long as you don't have another risky encounter, sperm can last AT MOST 7 days before ovulation (although not likely), then another 2 weeks for fertilization, traveling down the tubes and implantation and then another week or so for the test to pick up the hormone so it could be about a month after sex.
So if in a month you have a negative hpt, unless you are one of the very few who don't get positives when they are pregnant, then you are safe.
My oh and I hated condoms and I hated the hormones in birth control pills and such, so we used a spermicide gel insert (about the same price as condoms, no hormones, same reliability as condoms, but can be messy) and they worked for 8 yeasr until we were ttc.
