Well done OP. Try Runkeeper for an App, it's free.
But don't do double runs, it doesn't achieve anything fitness wise especially if you overdo it and hurt your joints or pull a muscle. Long distances definitely bring new issues like chafing, blisters and foot issues. Good quality socks and a very supportive sports bra are essential for anything longer.
It's a bit early for worrying about speed, just build overall stamina with regular running and speed will come. Try alternately some shorter slightly faster pace runs (even 10 ins is useful) that make you puff and where can't hold a conversation -with your current longer steady slow pace ones. This will help with your overall fitness level.
However if you really want to try some speed work, just speed up to proper out of breath pace then drop back to slow, several times. 1 min fast or even 30 secs to start with and at least 5 mins in between at slow. Also google 'fartlek' training.
You might find following a race training plan helpful, which sets out and explains the different approaches to building distance/time and speed. Some hill training also builds stamina, muscle and lung capacity too. There are loads on line - Couch to 5K is popular. I used Hal Higdon and even managed a few Half Marathons in my 40's (some years ago now sadly).
Thanks for reminding me how good running is - I must get out for frequently and stop making excuses!