I did exactly the same training for my half marathon – ignored the niggles then developed Achilles tendinitis.

No quick fix I’m afraid. I had to stop running for about three months (couldn’t even walk properly for two)

Research some Achilles exercises and stretches – they work. But you need to be committed and do them every day multiple times.

Find a good sports massage therapist. Mine is amazing – after two months rest I was able to start massaging and also used an infrared/laser machine that gets deep into the muscle area.

I also developed plantar fasciitis which is on the sole of your foot – mine happened when I’d done my Achilles and was walking differently to compensate. So to avoid that I had to freeze a small bottle of water and then use it as a roller under my foot daily. Hurts but works.