4 month regression beginning or end?

For about 1.5 weeks my almost 3.5 month old seemed to be going through regression, waking up every hour to 2 hours at night when normally she stayed asleep for 6 -7 hours before. She now seems to be sleeping 3 to 5 hours, is this phase still the regression? If not, will she go back to sleep for a longer period anytime soon or do I have to sleep train in order for her to do that? Anyone not sleep train and sleep was extended, if so when did that happen?