How do I tell if my constant distractions are from adhd?

Many causes. There are many causes of moderate to severe distractibility. If it has been present since before age 6, it is likely to be primary attention deficit (adhd). If it began later, causes may include poor sleep, daytime sleepiness, sleep apnea, depression, anxiety, anemia, use of drugs or side effects of medicines, onset of pre-dementia or mild cognitive impairment, etc.
Get exam and tested. Talk to your physician and get tested and a full exam. Remember that many of the symptoms of adhd, when taking in isolation, are problems that any body can have at any given time. It doesnt mean you have adhd. Adhd is a combination of symptoms, all at once, for a good period of time, present since childhood to some degree, and causing significant impact on the quality of your life. Get tested!
Talk to a doctor. Your doctor can refer you to a specialist who can do a full interview and give you a questionnaire to fill out. Being occasionally distracted is not enough to lead to a diagnosis of adhd but it can be a sign.
Absent minded. When the symptoms are severe enough to cause you to be significantly impaired, when the symptoms are not better explained by another mental or physical problem, and if they have been present for a while, then you might have adhd, but seek professional help before arriving at that decision.