Help please

Autumn

So my periods were regular they came the same time every month they were always 5-7 days long. However, my last cycle was 4 days and then this one is barely lasting 3 days. I know I could go to the doctor however we pay everything penny of the bill out of pocket and just can’t afford another $200 bill for it this month. Nothing has changed lifestyle wise so I have no clue what’s going on! If anyone has been in this situation please shine some light! Thanks in advance ladies.