sore boobs!

Rebecca • 27, TTC my second baby. I love my husband for giving me baby #1 who is the most amazing gift in the world!!
According to Glow I'm 6dpo and according to FF I'm 4dpo. I woke up today with sore boobs surely this is way too early? I never get this as PMS symptom, anyway else experience sore boobs this early on?