Your offense is holding you back.
My guess is that you're registering around 3-5 points in HR and RBI, and maybe 5-7 in BA, 7-9 in runs, 10-11 in SBs. You need some power, bad.
1. Find someone who will (unwittingly) pay a premium for the brand-name value of your outfielders. All 3 guys -- Heyward, Markakis, Kendrick -- have more "name value" than fantasy value, and you probably drafted the 3 between the 7th and 13th rounds, even though they don't perform like that.
Heyward is really a rich man's Will Venable; even this season, his 162-game pace:.273-88-14-66-58. Kendrick and Markakis are .285-80-14-70-15 hitters, at best.
Basically, your 3 OFs will combine for about .270-.280, 200-220 runs, 40-50 HRs, 180-200 RBI, 60-70 SBs. A trio of less heralded OFs of, say, Nick Swisher (.265-93-32-93-2), Gerardo Parra (.280-80-10-70-30), and Josh Willingham (.260-80-30-90-6) could combine for .270-.280, 220-240 runs, 65-75 HRs, 240-260 RBI, 35-40 SBs.
2. Target less-heralded OFs (i.e., guys who have more fantasy value than brand-name/real-life value) like: Nick Swisher, Luke Scott, Josh Willingham, Jordan Schafer, Cody Ross, Nolan Reimold, Alejandro de Aza, Mark Trumbo, J.D. Martinez, et al.
Swisher, L. Scott, and Willingham are guys who should get you .260-.270-85-30-90-5, and right now you don't have anyone on pace for 30+ HRs other than Carlos Pena.
3. You're wasting H. Kendrick's value by putting him in the OF. As an OF, he's average across the board. Either find a way to start him at 2B, or trade him to a team that needs and will pay you for Kendrick as a 2B.
4. Find a way to start Gerardo Parra. Parra's a .280-80-10-70-30 hitter, which is just as valuable as any of your current starters -- but don't start him until/unless you've traded away at least one of your current starters.
5. Consider trading/packaging Votto to upgrade at OF. I won't say that Votto is overrated per se, but I do think he's more useful to you as trade-bait than as a contributor.
Trading Votto would be a gutsy move, but you're in last place and you need to make up considerable ground in order to win your league. If it were H2H, I wouldn't try it, since you can sneak into the playoffs and then hope for a good September. But because it's Roto, you're either first or you're last.
You have Carlos Pena, who'd be more than capable as your 1B. Over the last 4 seasons, Votto has averaged .312-98-32-105-10 per 162 games. Over the same span, Pena has averaged .224-87-36-104-4. Yes, the batting average is a HUGE drain, but if you can trade Votto and significantly upgrade your OF, you'll likely gain far more in the other 4 categories than you'd lose in batting average.
For Votto and Markakis, you could receive an OF duo like Curtis Granderson (.270-105-35-100-20) and Nick Swisher (.265-90-28-90-2).
For Heyward, Kendrick, and Gardner you could probably get someone like Andrew McCutchen (.295-100-18-70-30).
Votto/Heyward/Kendrick/Markakis should combine for around .285, 300-320 runs, 65-75 HRs, 300-320 RBI, 75-85 SBs.
Pena/Granderson/McCutchen/Swisher shouldcombine for .260-.270, 360-380 runs, 100-110 HRs, 350-375 RBI, 55-60 SBs.
You might lose 4-5 Roto points in BA and 1-2 in SB, but if you gain 4-5 points in each of R, HR, RBI, you'll come out far ahead.
6. Get rid of Geovany Soto. At this point, not only is he a BA drain, he's not giving you anything. His BA is undoing a lot of what Votto and D. Wright have been giving you. He's got only 1 RBI, on one HR, and he's a lock to not steal a base all season (even the 2-4 SBs from the average catcher would help you).
Get a guy like A.J. Ellis, Carlos Ruiz, Chris Iannetta, Jarrod Saltalamacchia, Jon Lucroy, Ramon Hernandez.... At least one of these guys should be available, and any of them would be a monumental upgrade over Soto.