Multiple night wakings

My almost 4 month old has been awake every hour since 6pm. Sometimes it's even less than an hour (after feeding and putting her in the cot she'll be awake after 15 minutes of putting her down!). This went on until 1ish am when she did sleep 3 hours after. We're at our wits end. I'm wondering why she was waking up loads? Could it be that my breast supply isn't enough or something else ? Is this the 4 month sleep regression?