You asked

I've heard you can buy breastmilk online - is this safe?

Mums understand the benefits of breastfeeding and may look at online sources if they find they are not able to produce enough milk themselves; but scientists have deemed the practice of buying unpasteurised milk online as unsafe, as it may put babies at risk due to possible bacterial or viral contaminations.
If you do find yourself struggling with your baby’s feeding demands, rather than resorting to buying online, why not try our top tips:
Don’t get down about it.
While breastfeeding may come naturally to some mums it might not be the same for you. Talking to a family member or friend who has gone through the same experience may help.  
Discuss any concerns with your midwife or GP.
Always be honest with how you are feeling - they are there to help and advise you.  They will likely give you tips on how to boost supply or offer alternative ways to feed.
Always feed on demand.
Your baby’s sucking will stimulate your breasts to produce more milk.
Add a pumping session between feeds.
Milk supply may decrease if feeding is interrupted for a period of time so stimulate your body to produce more by pumping between feeds. You can then store any pumped milk in the fridge or freezer until your supply increases.

Try breast compressions.
This may help mums increase flow to baby and completely drain the breast. Switch between the left and right breast until your baby is satisfied.

Mums often worry that the natural bonding process between mother and baby can be affected if they don’t breastfeed, but by playing, cuddling and holding your baby close you will still be able to create an unbreakable mummy infant bond.

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