Clear liquid coming out of breasts is usually due to a hormonal imbalance and that same hormonal imbalance can make our period late which is really a longer cycle than our norm. However, since you had unprotected sex, you need to take a home pregnancy test. These can bought almost anywhere. Let us know what it says.
In truth, it's very doubtful it is actually milk. Women who deliver babies do not have their milk come in until a couple of days after giving birth. You likely have prolactemia which is like lactation but due to hormonal imbalance. I guess we will see what the ultrasound says but am guessing you are not going to turn out pregnant unless pregnancy has thrown your hormones off. If you aren't pregnant, get hormone levels checked. Too much estrogen production can make our cycles long and prolactemia happen. good luck
I'm an adult whose had children as well as prolactemia. :>) Prolactemia IS lactation but it is not like baby's milk and caused by hormonal issues. You can confirm with your doctor about that. Lactation is kind of 'like' milk I guess but it is due to hormones and not what happens after you have a baby to feed your child. And leaking nipples is not a sign of early pregnancy.
I've had the same thing as you describe. I did the pregnancy tests, major worry over it and saw several doctors. I ended up with an MRI to see if I had a small tumor that causes this type of lactation from the nipple which I did not have. I had blood work which showed I had too much estrogen production and a slow thyroid. Those combined were causing my leaking of nipples. I was seeing an endocrinologist when my issue resolved on it's own. But an irregular period is also a sign of the above issues. If you were irregular before this, probably a hormonal issue going on. Just trying to help. good luck