My ds is 6 and has been with us almost two and a half years. He almost always ends up in tears at home time. We rarely go to the park, he doesn't want to go.
Over the last two and a half years I've thought the pattern of getting angry, crying, fighting with his sister (our birth dd) at home time was because of factors like dd winding him up, or him getting cross with her!
I now feel that it is the same pattern he exhibits (on a smaller scale) when there are any changes at all! Like going from watching TV to not watching TV, from not eating dinner or breakfast to eating dinner or breakfast, going to bed, etc etc.
So I would second what the others say and avoid the park/interaction with other kids at this stage. If there is another way to go, could you go it?
If not, can you maybe change the routine a bit and have some park play at weekends, one to one with your partner (if you have one) or with you while someone looks after little sibling?
If your ds is very cross about not going to the park you could make sure that an activity at home, in the garden, is planned and you can say 'Remember we are going to plant some seeds, build a den, watch that special programme, go on the (CBBEBIES, or whatever), website etc."
Seven weeks in is very, very early days and it's very important to build in some time each day with you, while he has the energy, so although parks are normally great this may be a case of lets wait for the weekend, or Friday or whatever, for the park after school.
Good luck. 