One of my all-time favorite Android apps is Chordbot. I've linked to the free version, there's a paid version as well. Just set up your chord progression, and figure your melody out while it loops.
On a whole other plane, but a very approachable one, you can get Reaper, an entire Digital Audio Workstation (DAW) for $60. (And if you don't pay, you just have to wait ten seconds every time you load the program, but you should pay, because they're awesome.) A DAW will allow you to create music however you want to; it's what they use in music studios. You can make music piano-roll style, or play a MIDI keyboard into it, or record vocals our acoustic instruments, and mix them all together.
Leveraging the power of a DAW has a pretty steep learning curve, but it's incredibly worthwhile. Once you get it configured, and you download a bunch of virtual instruments (VSTIs), you'll be amazed at what you can do.
I know it's more complex than you were probably wanting, but learning to use a DAW will open up infinite possibilities for you. Put up with a couple of weeks of frustration, and even without a musical background, you can really start using the tools in the DAW in your workflow. It won't end up just being a crutch; as you learn more about music, knowing about how to use a DAW is invaluable.
/r/Reaper has a few tutorials in the sidebar, and you can find tons of helpful information on Youtube. You can also check out other DAWs that might suit your style better; I've been using Ableton lately, which is astounding. Reaper is a great place to start, though; grab the 30 day demo and start messing around. Read through the manual, do a few tutorials, and I think you'll find it worthwhile.