What Causes Intermittent Heavy Periods With Cramping?

Im 23 yrs old, I have some symptoms of pregnancy but also I have started my monthly cycle. The first day wasn't as regular as the past, it started and continued on and off for two days very light and stopped for another two days completely. Then started again heavy with painful cramping for a day and a half then almost nothing. I get dizzy very easily, I continue to eat even after Ive had a full meal. Is it possible if I were to take a test, would I be able to get a proper result or should I wait until I completely finish my cycle?