Berry, I would recommend that your see a periodontist, especially as you have good oral hygiene habits. Receding gums can be quite serious, and it's important to stop them in their tracks if at all possible. A periodontist is the best person to do this for you. You will be fine to have treatment while pg, but as Suse said, it's best to get this under control beforehand, as pg hormones can exacerbate the situation. You can't grow the gums back, but hopefully you can stop it from getting worse. If things really deteriorate sometimes gingival grafting can be done, but that is a last resort measure.

Root canal treatment is undertaken when the nerve in a tooth is dead or dying. It's not related to gum disease, and I can't think of any situation where one would have root canal treatment because of receding gums! In fact, if the situation with the tooth (gum-wise) is not looking healthy, one would be reluctant to undertake RCT (in the case of a dead nerve) in case the periodontal disease deteriorates further.

You will need a referral to see a periodontist, so you will have to see your dentist first to obtain that. In the meantime, if you are not already, try using some sensitive toothpaste (ie. sensodyne, or colgate sensitive) and see if that helps a little. One thing your general dentist can do is apply some desensitising solution to the sensitive area, that be effective for some months.

I HTHs, please sing out if you have any further questions.