Acid reflux is something that happens involuntarily. A person may feel some acidity or bitter taste in his esophagus but it does not reach the mouth. In this case, it does not break your fast because it does not come out to the mouth.

Chewing gum which contains sugar and artificial flavorings breaks your fast. But if the gum does not contain any substance that will dissolve and enter the stomach, then it does not break the fast.

Intercourse at night in Ramadan is permissible. Night lasts from when the sun first sets until (true) dawn comes. It is haram to have intercourse with your wife during the day in Ramadan and it is one of the things that invalidates the fast.

If you cannot help vomiting, your fast is valid. Also, swallowing vomit unintentionally does not break the fast.

Blood tests do not invalidate the fast, rather they are forgiven because they are something that is necessary and they are not like the things that are known in Shari`ah to invalidate the fast.