First of all, get rid of all that annoying ticking before the melody comes in at the start. Then, remove a lot of the repetition and make your changes stand out more. Five minutes into a song is too late for a dubstep drop. Focus on dynamics. Start off quiet in a 20-40 second long intro that gradually increases in intensity and volume. Then, with your first verse of the melody, which should be about 45-60 seconds long, have a nice, memorable melody that shifts every 8-12 seconds. Then, you need a section where it all slows down and gets quiet, which should basically involve removing and fading out certain parts of the melody over the course of about 15 seconds. From there, you should have a short little interlude, maybe a piano or strings section, lasting 10-20 seconds. Then you should start building up to your drop by adding in a reprise of your melody on top of that interlude, lasting about 15-25 seconds. Key here is to really focus on building intensity through volume, composition, and maybe even tempo if you want. Then, at it's peak, have a 1-second long extended note or something of the sort, kind of hanging in the air. Then do a drop. The drop should last anywhere from 30-70 seconds. It depends on how important you think it is. Make sure you have even more variation here than anywhere else basically. It's also a good idea to follow the general pacing and rhythmic pattern of the melody, and you should throw in a few chords from there every now and then to tie it up. Avoid making it just a copy of the first verse with some harder drums or random sounds. That NEVER works. Take it seriously and spend some time on it. After the drop, you need to move on to another bridge. Return to another quiet interlude with a quick (3-5 second-long) fade. Then, once you've faded it out, over the course of the next 10-15 seconds you should build back up into a verse 2 of your original melody. This should be about the same length as your first verse, with the same or similar instruments. Avoid making it just like the first verse, though. You should add a bit more. Change up the drums, add another arp, or something. Maybe both, and a little more. When your 2nd verse is done and if you just want a song with one drop, go ahead and have a breakdown in intensity. Over the course of 8-12 seconds, get to an interlude which slowly gets quieter and then fades out.
Now, I'm not saying you need to follow those instructions 100% of the way. Art is interpretive. However, the most successful melodic dubstep songs I've seen seem to follow a similar structure. It just makes sense. By the way, you have a nice melody. It just needs development. Try looking at Lockyn's work if you need inspiration. He makes house and melodic dubstep, and he's got it down to a science.