I would recommend designing the league for 14 weeks, as then it can be balanced with all pairs of teams playing each other exactly 3 times, and all teams having exactly 21 games. Then for the 15th the week, you are free to choose any 6 games you like. Here is a a possible 14 week schedule that you could use, teams are the letters A to H and the weeks are separated by the dashed lines:
F1 F2 F3
(A B) (D F) (E H)
(B G) (C E) (F H)
-----------------
(B D) (C F) (A E)
(B C) (D H) (E G)
-----------------
(D E) (G H) (A F)
(A D) (C G) (B H)
-----------------
(A G) (C H) (B E)
(B F) (D G) (A C)
-----------------
(A H) (F G) (B C)
(C D) (E F) (G H)
-----------------
(B D) (E H) (A F)
(F G) (C E) (D H)
-----------------
(A G) (B E) (C D)
(E G) (A H) (B F)
-----------------
(C H) (A B) (F G)
(D F) (A E) (C G)
-----------------
(F H) (D G) (A C)
(B H) (A D) (E F)
-----------------
(D E) (B G) (C F)
(C E) (G H) (A D)
-----------------
(E G) (B C) (D H)
(F H) (B D) (A G)
-----------------
(E H) (A B) (C D)
(C G) (A F) (B H)
-----------------
(C F) (A E) (B G)
(A H) (B F) (D E)
-----------------
(E F) (C H) (D G)
(A C) (D F) (B E)
Above all teams should play on each field exactly 7 times, and teams should also be as balanced for early and late games. Hope that helps.
