It really is very rare to have a medical condition that means with a correctly attached baby, fed on demand, you still don't have enough milk.
However undiagnosed tongue or lip tie, can cause such poor latch that baby struggles to feed and the breast is not stimulated enough to increase milk supply as the baby grows. Some babies have ties and it doesn't affect feeding at all but very painful latching with damaged nipples needs sorting ASAP.
Getting a good latch can be difficult and the resulting 'unsatisfied' baby can make you think that there isn't enough milk, but really if you get the latch right you can trust that your body WILL produce milk. (If you were one of the very few - and it is a tiny number - who had a medical reason that milk wasn't being produced sufficiently, then a medical professional would spot it as baby's weight and alertness will be monitored). Anything that interferes with a babies sucking on the breast can reduce milk supply (pacifiers, spacing out feeds, feeding formula instead of putting baby to breast).
Educate yourself on what is 'normal' behaviour:
Cluster feeds
Growth spurts
Frequent feeds
Poo colour changes
and watch some you tube videos of correctly feeding babies so you can see what the nose to nipple/wide gape looks like.
When we've not been surrounded by women breastfeeding it really is so difficult for us to relax in to trusting that what is happening is 'normal', 'natural' and 'working'. So check out local support groups where you can see/meet other Mum's who are breastfeeding and also find out where your nearest Lactation Support will come from.
I hope you won't need this support and it will all work out for you (I have met many women for whom bf just clicked but I myself had a lot of latch issues at first) but it is best to find it all now so that when you are feeling a bit hormonal and stressed out with a newborn you aren't also struggling to get the correct information.
There isn't a food that will magically give you milk if your baby isn't stimulating the breast by sucking but there are a few things that can help your body make milk more easily.
Stay hydrated
Eat things like porridge (good mix of fat, carb and protein)
There are supplements that people swear by, but OVER supply of milk can cause as many problems as under supply so I wouldn't advise taking any unless you know there is a problem. Over supply is very common in the early weeks (after your milk has come in) so you don't need to add to that.