Before I suggest you whether it is safe for sex during or after your periods and also about the emergency contraceptive pills, I will explain briefly the monthly phases of menstrual cycle so that you will have an idea. On average menstrual cycle is explained by considering it as a 28-day cycle which is the average for most of the women around the world. Day 1 is considered as the day where bleeding starts and from this day on, the menstrual cycle is divided into 4 stages:
1. Menstrual phase
This phase lasts for 5 days i.e. from day 1 to 5. The uterus will expel the inner lining of itself along with minor blood vessels in the form of menstrual fluid. This fluid along with blood comes out and this bleeding will last for 5 days. On average 10-80 ml of blood loss will occur. This phase will also induce abdominal pain, back pain etc. This is caused when the abdominal muscles and uterus induce a series of contractions to expel the menstrual fluid.
2. Follicular phase
During this phase, the ovarian germ cells will grow. This phase starts along with menstrual phase but lasts until 12 to 13 days. The ovarian germ cells will produce egg cells under the influence of the hormone called Follicle Stimulating Hormone (FSH – Released by pituitary), Gonadotropin-releasing Hormone (Gn-RH – Released by Hypothalamus of the brain) and Luteinizing hormone (LH – Released by Pituitary). During this phase, egg cells develop inside a sac-like tissue called follicle. The uterus will develop a lining around the follicle called as the endometrium. The endometrium is formed under the stimulation of hormones (usually steroid hormones such as estrogen, progesterone, and androgens) released by the follicle itself.
3. Ovulation Phase
This phase starts from the 14th day of every menstrual cycle. During this phase, the follicle increases the levels of estrogen. With the increased estrogen levels, hypothalamus of the brain will release Gn-Rh and also stimulate the pituitary to secrete Luteinizing hormone (LH). Increased LH will initiate ovulation and the ovum is released into the peritoneal cavity from the ovaries. The ovum is collected by fallopian tube. The ovum stays in the fallopian tube for a period of 24 hours if it is not fertilized. If not fertilized, it will perish. So your chances of getting pregnant are very high in your ovulation phase. If you have an idea about the ovulation phase, you can understand your fertility window.
4. Luteal Phase
When the ovum from the ovary bursts out of the follicle during the ovulation phase, it releases a scar on the ovary which develops into Corpus Luteum. This will secrete hormones such as progesterone to maintain the thickness of the uterine wall if the ovum gets fertilized. If fertilization does not occur corpus luteum will wither away around 22nd to 28th day of the menstrual cycle.
As you stated, your menstrual cycle began at 14th January and the intercourse happened on 19th to 21st. This does not have any fertility chances and is considered as safe. It is safe only if you understand your fertility window and according to the data given by you, your fertility window will be on 26th January. But remember the human sperm will survive for 5 days inside the female body and that is why emergency contraceptive pills are advised to be taken before 72 hours of the sexual intercourse. But you took the pill on 23rd and the sexual intercourse happened until 21st. Considering 21st as the last of intercourse, the sperm can survive until 26th which coincides with your ovulation phase. But you took the pill within 72 hours of the intercourse, it is fair to assume that conceiving chances are zero. But make sure to keep a track of the next menstrual cycle.
Using of emergency oral contraceptives without proper advice can lead to many side effects. Some of those side effects include headaches, dizziness, nausea, increased vaginal bleeding (inter-menstrual spotting), weight gain (most common) etc. Even Urinary Tract Infection (UTI) is also induced by excessive use of these pills. Sinusitis, on the other hand, made you more uneasy with its symptoms along with the side effects of the pills.
Avoid having unprotected sex. Always use condoms and I would suggest you refrain from having sex until marriage, if not married. Do not use contraceptive pills without a proper prescription or a physician's advice. Make notes of your menstrual cycle and try having an idea about the fertility window for your future reference.
Dr. V. Shashikanth