Hi!
Assuming your regular cycle is 28-30 days, the next blood release happening on the 10th day of your cycle is something out of the ordinary. There are a few indications to look out for to ascertain it is a period and not abnormal vaginal bleeding due to other causes.
1. Is the amount/flow, colour and consistency of the blood the same as a normal period?
2. Is the length of your blood flow i.e. 4-7 days?
3. Is there any spotting, blood lumps (dark sticky lumps) or other substances, including discharge that was observed?
4. Menstrual cramps? as per normal?
If your blood flow on the 10th day is as a normal period, and this is the first time this is happening, it could be due to changes in your diet causing any upset of the gut system, or it could be over-exertion of your physical self, for e.g. running a marathon. This is the more common condition in women, and you might have a weaker/more sensitive digestive system. We term this as 脾气亏虚 in TCM.
There is another side of the coin, which could be hyperactive inflammatory response, causing a sudden release of blood due to inconsistency of the blood from the hormonal changes. Such changes typically happen randomly and occasionally, mostly due to stress and lack of sleep/poor sleep. This is also known as 肝郁脾虚，or 血热。
However, if this blood flow on Day 10 does not present as a normal period, either it lasted for 1-2 days, may be spotting, amount is little etc, then we should consider Ovulation-bleeding (经间期出血）. This is an indication of the female sex hormones rapidly decreasing, causing abnormal shedding of the uterine lining. There is also the possibility of an overproduction of female sex hormones, leading to an excessive supply of blood to the uterus, and the response of the body to release the additional blood.
There are many possibilities to this situation, and it is recommended to seek a thorough consultation with a physician if this symptom continues for 3 period cycles or more. Sporadic abnormalities of period cycles do occur from time to time, we can observe the symptoms further and longer to come to a clearer diagnosis.
Hope all is well!
Cheers
Victoria
