Not much from the OP for a while, but let me chip this in.
First, I'm not an instructor and did my PPL about 20 years ago.
Second, some of this may have been said above and generally I agree with pretty much all that is said above, apart from stop if you don't enjoy it - there are always low-spots and things you won't enjoy both during training and afterwards, if you are passionate about wanting to fly you push through them, if you aren't you may not. But certainly if you have a prolonged dislike of what's going on you must reevaluate. Doing something different / with someone different / with less pressure are all good things to reignite the passion. Stating the obvious, but the only way to learn is to reflect on what went right / wrong and why.
Now, you leave out quite a bit of background that might help people here: what are you flying, where (general area if you don't want to mention airfield), how did the earlier parts of the course go prior to nav, any particular problems then? Specific feedback from the instructor rather than just "navigation bad".
One lesson every one or two weeks is simply a recipe for treading water for most people, you spend as much time relearning (and your instructor will probably have forgotten the last flight) as you do making progress. Fly at least twice a week so that the second lesson can consolidate and build on the previous one. If that means you have to stop flying for a few months while you save up enough to have a concerted go at it, still do that. Winter can be a problem - I basically stopped the PPL during the Winter due to weather (cloud/wind) and waterlogged field. There was a good degree of work to do in the Spring to get back up to speed, but a lesson a month that I could actually fly achieved nothing really.
I would expect your instructor to brief you before the flight and most certainly thoroughly debrief you afterwards; perhaps if things have been dragging on they have got a bit lax?
What would I do in your shoes?
1) If I am not getting detailed debrief on what's going wrong together with remediation plans and trying different approaches to crack issues from the instructor I would try another one - different airfield / area if you like, but stick to the same aircraft type.
2) Have some fun flying, whichever bits you most enjoy, to keep the dream alive.
3) Definitely try to get rides where you can practice navigation without the pressure of maintaining track.
4) Practice on flight sims at home - one with decent photo scenery of your nav areas, ability to give you some bouncing around and variable wind drift to require control input as well as nav. Not up to speed on what to use now, but back in the day I found it very useful for nav and IMC. Just getting your drills and skills down pat where you aren't paying several pounds an hour for the privilege is great - how you use your map, your plog, marked pencil or ruler for inflight nav checks, gross error check, drift correction and track regain, point it in a random direction go make a cup of tea then come back and try to figure out where you are - lots you can do. It's not the same as having to truly aviate / communicate at the same time, but it's great practice.
5) Get forensic on what's going wrong when you do fly - maybe try a head-mounted camera & the gps track record trick, give a running commentary on what you are doing and why when flying so you can review it yourself later.
6) Do practice Pan / lost calls with your instructor so you have the reassurance that if you are up there alone and get totally confused someone can help find you; try some QDM homing too in a similar vein.
7) Finally, if you are doing this in a congested area (e.g. around London), where you have to work about 5X harder with regard to airspace / communication / traffic issues, think about finding somewhere easier to get the basic skills right then build up to the higher workloads.
Let us know how you are doing.