Ammonia smell after running? Also, how to increase distance safely....

 So after my last few runs I have had this ammonia smell in my nose, I asked my husband to smell me (yeah, and he is a good guy and he sniffed me even after I had just run four miles LOL), he said he could not smell that smell ON me. After about 10 mins of rest the smell went away (even without me taking a shower), so I know it's just a smell I am smelling in my nose. I am afraid to look it up with Dr. Google for fear of what might come up LOL Any guidance on this would be awesome. 

Also, I have felt lately that the distance of my runs has become "comfortable", meaning I can easily do 3.5 miles without strain or pain or really having to push myself. I would like to increase my distance but I don't want to push to hard to fast and hurt myself. I have thought about the Bridge to 10k, but I feel like going back to running intervals is a step backwards (might be stupid, it's just the way I feel). So how did the longer distance runners build up to those distances? All advice welcome! 

 Not sure what you smelling ammonia is but if YOU SMELL LIKE ammonia it means you are using protein as your primary fuel source, which is not an ideal scenario.  You smelling it may be a warning that you are getting close to the point.

My wife hates being in the same room with me after I workout, because of the ammonia smell.

Most "experts" suggest increasing your mileage by about 10% a week.  For most new runners that is adding a mile to one run a week.  If you are looking to do a 10K, I'd  run what you normally do and add a mile to your long run day (usually on the weekend).  After you get comfortable that you can finish the 10K, you can start adding miles to your other runs.

As far as intervals, you are going to want to use them when you want to start running faster.  My favorite workout is mile repeats.  I run a mile at a particular speed (usually slightly faster than my 5K pace) and walk for 3 minutes before doing another.  You can do the same thing with 400 or 800 meter repeats.  To run fast, you have to train fast but it sounds like you are a bit away from that still. 

I'd go sign up for that 10K today!