I've had this. it was really starting to kill me but just in the last few weeks we've managed to consolodate a period of good health and night weaning to produce a properly sleeping through DD (she's 18 months). It still took several weeks for me to be able to go back to sleep if I woke (whether woken by her, or on my own).
Things I've learned:
My insomnia is a manifestation of chronic overtiredness. So taking action as soon as i can to break that cycle really helps.
i follow the recommendations in the back of the No Cry Sleep Solutions book. Doing the recommended stuff, especially sleep cramming (going to bed early, napping during the day whenever possible) does really help.
For me, so too do some sleep remedies. At the moment i take a valerian tinicture every night as i go to bed (got it from Holland and barret, I follow the instrucitons on the bottle). It helps me to sleep well, it is also helping to dial down my nerves which were starting to feel like they were permanently set on red alert after a stressful year of becoming a mum / moving house / being very ill ( a week in hospital when DD was 4 months) / going back to work in a new job when DD was 7 months. So when i did wake up it was almost always with a panicky jump.
In the last few months, i've also taken the Boots over the counter sleep drug, I think they call it Sleep-eze or something to help break the cycle. it comes in two strengths, I have the lower one, and only take one pill, sometimes. At the height of my insomnia I have once or twice taken a second pill in the middle of the night (which is within the dosage recommendations). Every now and then I've taken it several nights in a row but I have learned that if I have an insomnia bout (my problem isn't going to sleep, but that if I wake in the night I don't go back to sleep) if I take it as soon as that starts, just the once or perhaps a couple of nights of it breaks the vicious cycle of over tiredness. And then I stop (the worry with all sleep inducing drugs is that they can be addictive).
I am still breastfeeding DD. The leftlets for all these things will say do not use while breastfeeding. After a week in hospital when was on hard core antibiotics and we carried on feeding, I've got much more relaxed about those recommendations which in general mean 'we've done no testing so don't blame us if you have problems'. You must make your own decision, but I can report DD is fine.
Just this last week I have started sleeping seven hours stretches with just the valerian. This is the first time this has happened since I was pregant, so getting on for two years ago.
OP, you don't necessarily have to stop breast feeding. if you want to carry on, you could consider night weaning (we started this at a year, but looking back maybe could have done it more easily a bit earlier - about hte stage that you are now).
On the other hand, a well rested mum is happier and much more able to be a better mum. So if moving on from breast feeding would help you achieve that, do it.
Also bear in mind almost all young children go through periods of night waking. DD has only just started sleeping through now, but then has almost all her teeth. So from age 8 months to now she has been teething (and so night waking) more often than not, so that really drove my insomnia. it won't necessarily be that way for you - you might get a few months of good sleeping soon, if so use that to try and recharge and restore yourself, so you can get through if another period of night time distruption comes a long.