I defined a function, but it takes a long time to show its result. It will also take long time to use this function later.

p1[x_, t_] := pinf + (A2 (-1 + E^(-t \[Theta]c)))/\[Theta]c + \!\(
\*SubsuperscriptBox[\(\[Integral]\), \(0\), \(t\)]\(
\*FractionBox[\(A11\ 
\*SuperscriptBox[\(E\), \(\(-
\*FractionBox[
SuperscriptBox[\(A10\), \(2\)], \(t1\)]\) + A3\ \((\(-t1\) + t)\) - 
           t1*\ \[Theta]c\)]\), 
SqrtBox[\(t1\)]] \[DifferentialD]t1\)\) + \!\(
\*SubsuperscriptBox[\(\[Integral]\), \(0\), \(t\)]\(\((\(-A8\) + A9 - 
         A15\ 
\*SuperscriptBox[\(E\), \(A3\ \((\(-t1\) + t)\)\)] - A9\ 
\*SuperscriptBox[\(E\), \(\((t1 - t)\)\ \[Theta]c\)] - A16\ 
\*SuperscriptBox[\(E\), \(A3\ \((\(-t1\) + t)\)\)]\ Erf[
\*SqrtBox[\(A5\)]\ 
\*SqrtBox[\(\(-t1\) + t\)]])\)\ \((
\*FractionBox[
SuperscriptBox[\(E\), \(-
\*FractionBox[
SuperscriptBox[\(A12\), \(2\)], \(t1\)]\)], \(
\*SqrtBox[\(\[Pi]\)]\ 
\*SqrtBox[\(t1\)]\)] - 
\*SqrtBox[\(Dp\)]\ 
\*SuperscriptBox[\(E\), \(\[Alpha]1\ \((2\ A12\ 
\*SqrtBox[\(Dp\)] + Dp\ t1*\ \[Alpha]1)\)\)]\ \[Alpha]1\ Erfc[
\*FractionBox[\(A12\ 
\*SqrtBox[\(Dp\)] + Dp\ t1*\ \[Alpha]1\), 
SqrtBox[\(Dp\ t1\)]]])\) \[DifferentialD]t1\)\) /. {A10 -> (-lh + x)/(
      2 Sqrt[Dc] ), A12 -> (-lh + x)/(2 Sqrt[Dp ])} // Simplify // 
  Normal

ep1 = p1[x, t][[1]]

ep2 = p1[x, t][[2]]

eq3 = p1[x, t][[3]]

eq5 = p1[x, t][[4]]