Dear Lollyheart
It does indeed sound like blocked ducts.
Your baby will still be able to get some milk out, and it is essential that you feed first from the affected breast, even if it is very tender.
You could also try applying cold compresses between feeds (try using frozen peas wrapped in a tea-towel) to reduce the inflammation, as well as regular ibuprofen. Use warm, moist compresses immediately prior to feeds, to vacillate the ducts and help the milk flow.
If your ducts have not cleared in 24hrs, you should probably try the flucloxicillin, although if you can get your GP to do you a repeat prescription and get someone to collect it for you, that would probably be easier. You need to rest up and take it easy.
Blocked ducts are not always caused by a poor latch; ill-fitting bras and clothes/bag straps can cause it (sleep without a bra, use a muslin under a t-shirt to soak up the milk! and try to sit without a bra for a while, again with a muslin to help with leaks). Also if your baby positions his hand against his face, if it pushes onto your breast that could cause blocked ducts (usually with older babies). Sometimes it is just a question of over-supply of milk, you might be producing a lot and your baby is not yet big enough to "clear" the breast. Of course, it could be down to "latch", so it might be helpful to get a midwife, or breastfeeding counsellor to come and have a look tomorrow if you can.
If you think you are oversupplied (perhaps the last bout of blocked ducts was on the same breast it could be the case) you can use a savoy cabbage leaf (take one from just under the outer leaves, crush it with a rolling pin or score it with a knife, then wear it in your bra for 20mns, up to 3 times a day. This is very effective at reducing the milk supply so use with caution if you intend to continue BFing. If the cabbage is out of the fridge it is a blessed relief too!
If you can have a warm bath, or a shower before a feed, that will help too. Point your body away from the stream of hot water, the steam and warm moisture will be sufficient without directly hitting & inflaming your breast tissue.
I know you must feel so demoralised by this experience, you are tired, sore and feel like throwing in the towel. No one will blame you if you do. However, to be honest, the best thing you can do is feed from the affected breast at the moment and make your decision to use formula when you are feeling more in control of the situation.
Make sure your DP knows how much you need help at the moment. If you develop mastitis you will need nursing so that your body can fight the infection. Even with blocked ducts you need lots of love & care.
FWIW I had blocked ducts 3 times with DS1, which led to 2 bouts of full-blown mastitis. Also had blocked ducts twice with DS2, and one course of antibiotics. In both cases I persevered and after 10wks in both cases had no reoccurence (I think when the babies got bigger, they sucked better and the milk supply was more in line with their demand, IYSWIM). Once you are past this horrible stage, breastfeeding is a real pleasure, and a wonderful way to bond with your baby, as well as free, convenient, and healthy for both of you.
But you know all that cr*p already - or else you wouldn't be putting yourself through this pain, anxiety and discomfort. Just hang on in there, get support & help, and let us know how you get on. No-one knows how hard breastfeeding is until they try it - it's why the percentage of UK babies who are BF at 6 mths is something incredibly low like 1%. If you eventually decide to use formula, don't waste too much time beating yourself up over it, but if you are determined to breastfeed, you can get through this difficult stage, and in another month or so, it will be a lot easier and even pleasurable!
Good luck