I'm not quite sure about your question, but if you wanting to chart to avoid pregnancy it is very important to learn from a certified instructor. Charting to avoid is quite different than charting to conceive.
But to answer, there are several ways to check for mucus - and internally is actually the least accurate. During times of infertility in a woman's cycle, the mucus dries up as is passes through the vagina over glands called the Pockets of Shaw. If you go looking for it internally, you will think you are fertile more than you really are because it disrupts the process that the mucus has to go through. If you would like to check your cervix, just to it at the end of the day and ignore any mucus you find inside!
As for how to check, there are lots of ways. The Billings Ovulation Method reccomends paying attention to what you FEEL as you walk around during the day because the nerve endings at the vulva are so sensitive that you can feel mucus when it takes 10 times the amount to actually see it. You might start to feel wet a day or two before you actually SEE any mucus - and this is very important for avoiding pregnancy, because that feeling of wetness means your fertiltiy has begun! Of course, you also jot down anything you happen to see.
Other methods reccomend looking at the toilet paper before and after you go to the bathroom and describing what you see.
ALL MUCUS IS POTENTIALLY FERTILE!!!! ALL MUCUS! Sticky or creamy or "less fertile" mucus has the ability to keep sperm alive and lock it away for up to 5 days while your body waits to ovulate. The mucus produced closest to ovulation, that which is slipppery or clear, unlocks the sperm and creates channels for it to travel quickly to the ova.
Some women have infertile vaginal discharge that is not fertile, but is similar to sticky/creamy mucus. This is called a Basic Infertile Pattern of Discharge. In order to accurately identify a BIP of Discharge, you need 3 full cycles first! You can't assume anything is infertile until it is proven to be so according to a scienticially proven set of protocols for evaluating it (a teacher can help you with that!)
So if you want to avoid pregnancy, then yes - at this point the only thing you can consider infertile is dry days. These are the rules for avoiding pregnancy:
1. Intercourse is available on alternating evenings after your period AS LONG AS YOU REMAIN DRY. If you feel or see any mucus or spotting, abstain until you have 3 full dry days again. The reason for alternating evenings is so that you have a full 24 hours for seminal fluid to leave the body, and then another full day to make mucus observations again to be sure you are still dry. So if intercourse happens on Monday evening, all day Tuesday for fluid to leave the body, all day Wednesday to make sure you are still dry and don't miss the beginning of your fertile time by accident.
2. Once ovulation is confirmed, you are infertile from the fourth day past your fertility Peak. That's because there is no way to know the EXACT day of ovulation except by daily ultrasound. Charting gives us a very close estimate, but it's still only accurate within 2 days. If you happen to ovulate 2 days after your fertility Peak, then the egg lives for 24 hours, that makes 3 days. So by day 4, the egg is definitely dead and the rest of the cycle is open for intercourse - even if you notice mucus or discharge. You get to ignore it afer Peak has been confirmed! Dry days only matter during the pre-ovulatory part of the cycle. And boy, do they matter!
This is probably a lot of information in one sitting. Again, much less confusing to learn from a teacher who can walk you through it all! To chart to achieve pregnancy, one only needs to know the basics. To avoid, there's a lot more that goes into it!
P.S. It's normal to have a lot of sticky or creamy mucus coming off the pill because the pill damages the part of the cervix where mucus is produced and it just takes some time to heal completely to make good quality mucus again.
P.S.#2 OPK's are really fun too! But be aware that they don't give enough advance warning for avoiding pregnancy. Use them to confirm your charting, but don't rely on them for when to start abstaining - it would be too late.
P.S. #3 - Teaching information in Ontario:
http://www.naturalfamilyplanning.ca
http://www.fertilitycare.org/locations/ontario.htm