First thing, you've done really well to breastfeed exclusively up to this stage and establish a good supply. Its usually always possible to increase supply once breastfeeding is established but it can be hard work. The first thing to address would be whether baby is actually not getting enough - the only way to really check this is by their weight gain - you can get your local health visitor to help you check this or if you have some baby scales at home. There can be other signs like open hands after feeding instead of clenched fists but I think these are maybe less reliable. Baby might just be going through a growth spurt and wants more from you at the moment, but the number one thing that will produce more is letting him on the breast whenever he wants, in a growth spurt this cluster feeding is what boosts your supply.
Breastmilk production works on demand, so the only way to produce more is to empty the breast. If baby isn't getting enough milk, the first thing to check would be the poor latch that you've identified, this isn't baby's fault, it just means he needs your help in improving his latch - you can get help from a lactation consultant or your local breastfeeding support with this, but there are a huge amount of YouTube etc videos to help improve your latch, and it might be a case of changing positions etc to see what works to help him drain the breast most effectively. Check out hand compressions while feeding to help with this too.
The other way to boost supply is by pumping, like you I can never get much from an electric pump, some women have better success with a hand pump or you can check some videos and guides on hand expressing. To help increase supply, ideally once you've improved the latch issue and have breastfed baby, in between feeds empty the breast through pump or hand expression, hot compresses can help the milk letdown. If you want this extra milk particularly in the afternoon you would have to focus on emptying the breast at that time of day - you could power pump in the afternoon to mimic cluster feeding, even if you don't get much anything taken from the breast will force the breast to produce more.
Lastly, you can try taking galactagogues - these are foods/supplements etc that are thought to boost milk - my lactation consultant advised fenugreek capsules which you can get in Holland and Barrett, so that might help. I would check out some of the guidance on the La Leche League website on increasing supply too, they have some really good resources.
Hope that helps a bit!