I'm having great difficulty with generating the shear and bending moment diagrams for a wingspan. I am using the elliptical pressure distribution equation; however, this problem doesn't consider a density or velocity. 
I have a lift of $50000 N$, so I have found $P_0$ to be 4244. Now I have segmented my aircraft span into $0.05m$ segments from $-7.5$ to $7.5$. I am calling this $dy$ (0,0.05, 0.1 etc...). I can then use my $$p(y) = p_0\cdot\sqrt{1-(4y^2/b^2)}$$ 
to find the pressure at all $dy$ points of the span. This plot looks fine and is elliptical. 
Now the area under this curve should be the shear force. So, my thinking is to integrate the $P(y)$ equation over area. I believe this will just become the following 
However here my area is actually my $dA=dy*c$ ($c$ = constant chord length across span of 2m) AND for $y$ I'm using my segmented $dy$ values, which feels wrong as I'm actually integrating over $dA$ and the 
is actually using 'A' and 'y' - not the discretised values, although I'm not sure that 100% matters? Anyway, this gives a decent looking graph I think, for shear vs span 
- Although I'm not sure it is right. Finally, I cannot work out the bending moment calculations and cannot get a decent looking graph. Have been going in circles online looking for methods but can't seem to remember the key steps of numerical integration for these kinds of problems. Any help on both the shear and bending moment diagrams would be greatly appreciated as this is driving me insane!!
Edit: If I were to integrate over dy Integrating over dywhich looks exactly like the pressure graph and not shear force.
EXCEL SNIPPET: Net Pressure Force (Pressure(y)/dA) vs Span
