I also had a lot of issues with mastitis and blocked ducts. It became my mastermind subject as I think I read every single thing I could on the internet! Like pp I became more accustomed to the feelings indicating there was a problem and acted early.
It helped to think about the mechanics of it. Basically you have a deposit of hardened milk somewhere in the tube, and you have to get it moving. Antibiotics clears any resulting infection but if you don’t break up that clog of milk, you will continue to have problems in that area. I also believed that I had some scarring or damage to my ducts in places that had mastitis and hence milk would collect and solidify there - who knows if that’s true.
With any hint of tenderness in your breast, you should use moist heat. Baths work best but when it’s not possible you can dunk your boob in a jug of hot water, or take a shower. Dry heat like hot water bottle helps too but not as good. You need to massage from behind the tender/vulnerable spot, with firmness down toward the nipple. Milk ducts unfortunately don’t always follow a straight linear path but massaging near it should help. Often the pain is concentrated very close to the nipple anyway.
Sometimes you can actually see thickened clogs at the nipple, which you can massage/squeeze out. Or if really unlucky, you could see a ‘bleb’ which is white skin grown over the end of the duct - I used to release these with a pin which is as horrific as it sounds, not recommended.
Ultimately, you need to be regularly massaging your breast and expressing as above. Oh and haven’t said of course feeding the baby on that side - works best in combination with moist heat just before feeding, so they can help you clear whatever you have broken up. Sometimes you may not know a blockage has cleared after a massaging/feeding session, and you just feel better later. Other times it’s really obvious and like a sense of palpable relief. The symptoms of fever etc can disappear very quickly.
As an aside I actually developed a blocked duct a few months ago, 2 years post stopping breastfeeding. GP was amazed and I assumed it was to do with how dodgy the inside of my ducts were after all they went through! To comfort you, most of my problems were in the early months like you and it would happen more occasionally after - I breastfed both of mine happily to 2 and nearly 4, despite all this, so hang in there if you want to. I also wonder if my issues were related to oversupply, as that was chronic for me - is this an issue for you?